There's one argument I tend to really dislike even when it's trying to argue for the same side as me and, to give a loose example, that argument is usually something along the lines of "You can't believe that this character could survive a 100 ft drop onto their head and survive because it's too unrealistic, yet you have no trouble believing that dragons exist? The story is already unrealistic!".
I dislike this argument because, be it intentional or not, it's an argument in bad faith. Just because a work of fiction is unrealistic in some ways that doesn't mean that it's unrealistic in every way and that anything goes.
And the reverse is true as well, where a story being realistic in some ways doesn't mean that everything is realistic, nor does that mean a story can have anything happen just because of the excuse that it's "more realistic".
The simple fact is that no story can capture every aspect of reality or the human experience. Even for a work that's trying to be as realistic as possible that's still far too big and broad to fit within a limited narrative, to say nothing about how plenty of stories don't want to be that anyway and likewise shouldn't be expected to be.
You need to let the story establish for you what would or wouldn't happen in its world, and I think this is something some people can really struggle with, causing them to make assumptions and insert ideas and possibilities into a story that the story itself does not encourage them to.
Some realism doesn't mean all realism:
I found it so bizarre how depressed I was seeing some people act after the Avatar Aang movie came out because of how Aang and the gaang had drifted apart so much...which they didn't and the movie gave no indication that they had. One of the people I talked to said that with how most of them live in different areas of the world in a time period without phones or airplanes the five probably can't see each other that often and thus would naturally drift apart more and more as time passed, which sure, that is probably what would realistically happen...but that's not a conclusion the story is at all leading the audience towards.
In the movie everyone is still presented as great friends who all get along as well as if not better than they did in the original series. Everyone immediately dropped everything they were doing to go help Aang when he asked, including the Fire Lord who runs an entire nation. Aang and Zuko are in frequent enough contact with each other that Zuko can just casually complain about his annoying attendant. For f**k's sake, Aang and Katara live together and sleep in the same bed. Yes, there is more physical distance between the gaang than there was in the original series (where they were around each other all the time because they were on a quest to save the world) but nothing even remotely implies any emotional distance or that their friendships have grown apart, and just because it'd be more realistic for that to have happened isn't a good enough reason to assume that it did. Especially for a series that has lines like "Some friendships are so strong they transcend even lifetimes." and in general shows how much value some people place on friendships even when they're nations apart or 100 years apart. It doesn't matter how "realistic" it may be, if your interpretation of events doesn't fit with what we're actually shown and how things normally go in the story, then that's probably NOT WHAT HAPPENED.
Or as an example of how edgy these interpretations can too often be, when Midnight died in the war arc of My Hero Academia, both when it originally happened in the manga and again when it was adapted for the anime, there were a noticeable number of people speculating that she'd been raped before the villain killed her.
Setting aside the possibility of it just being some of these people's barely disguised fetish, we are never shown her body, just her students' reactions of deep sadness that she's dead, and there's zero indication before, during, or after her death that this is what happened to her, so it seems like the only reason any of these people thought it was even a possibility that it did was just entirely because "Well, she's a woman and it'd be realistic that an evil person would rape her before killing her.", even though MHA never established something like that as a threat or possibility in its world facing the characters. Death or dismemberment, yes, and the war arc further reenforced that, even if only by a little more, but not sexual assault. Even with Endeavor and Rei the story went out of its way to show that Rei did want kids and did consent to having them with Endeavor. At most there was maybe coercion, which is obviously still bad, but he didn't force himself on her like some people think the villain did with Midnight.
It doesn't matter how "realistic" you think it'd be for it to have happened, if it doesn't fit with anything we've been shown of the world or story, be it the events, the dialogue, the tone, etc. then there's no reason to believe that it did happen.
It's the same problem with theories that speculate that a character is an unreliable narrator just because it's only them sharing their POV of something or that the entire story we're being shown is just in the head of someone who is either dreaming or insane. When the only basis for the theory isn't any actual evidence from the story but just simply that it could hypothetically be true since there's nothing to directly argue against it, it's not a good theory. Generally speaking, stories will give the audience actual reasons in either the text or subtext to suspect that what they're being shown isn't real or what actually happened. It doesn't matter how much more "realistic" it would be for the bizarre and unrealistic events of Foster's Home For Imaginary Friends to be taking place only in the head of Frankie, who is really an abused autistic child disassociating from the world, there is nothing in the show that even remotely points the audience in that direction, especially compared to the conclusion of "This is just a f**king weird world where imaginary friends are real and can be adopted.".
An unreliable narrator or "It was all just a dream!" needs more than just the hypothetical possibility that they could be the case, the story itself needs to provide SOMETHING to be a foundation for that theory. Otherwise basically ANY story can be being told to us by an unreliable narrator or exist only in someone's head and thus nothing we're ever being told or shown is what's actually happening in the story.
And then there's the people who go so far in trying to insert realism that doesn't fit a story that they'll essentially insist on the story outright ignoring the things it set-up that make it different from our reality.
There are people who non-joking argue that Akechi murdering Okumura in Persona 5, even if it was just to frame the Phantom Thieves, was ultimately for the greater good because Okumura was an evil CEO who viewed his employees and even his own daughter as disposable tools who he treated horribly and he was involved in a conspiracy that caused the deaths and/or psychotic breakdowns of multiple innocent people, and since in our world those kinds of people don't tend to change for the better the only real option was for him to die...even though the entire PREMISE of Persona 5 is the Phantom Thieves discovering the ability to change a person's heart by stealing the very desires that make them want to do terrible things, thus getting them to feel remorse for their actions and become better people! They have a 100% success rate with every person they've done this to, Akechi knows it works because of three separate cases where he's seen it works, and the thieves just got done doing it to Okumura when Akechi came in to kill him. There is zero reason to believe that Okumura wasn't also about to change for the better and at least try using his money and power and information he knew about the conspiracy to make up for the terrible things he'd been doing. Yes, it's sadly not a realistic outcome in our world but it's well-established to be a very realistic outcome in the story's world! So no, the more "realistic" option of Okumura being murdered was NOT for the greater good!
Some unrealism doesn't mean all unrealism:
But, like I said, this is a problem that also goes in the other direction too, where rather than inserting realism that doesn't fit the story you get people who think that a story being unrealistic in some ways means that it can be or even is unrealistic in all ways, even in ways that don't fit the story either.
When the Helluva Boss episode "Ghostf**kers" dropped I saw people who seemed like they genuinely couldn't comprehend the idea that ghosts don't exist in the Hellaverse. The idea seemed to be that because demons, angels, and magic exist in this world, all of which are unrealistic things, then there's no good reason for a character to be so disbelieving that ghosts exist too, let alone for the show to outright confirm that they don't.
Except not only do demons, angels, and magic not inherently have anything to do with ghosts outside of being supernatural, the lore of Helluva Boss and Hazbin Hotel is that when humans die their souls go directly to either Heaven or Hell and cannot leave, meaning a soul staying on Earth as a ghost would directly go against the established worldbuilding.
Someone made a pretty good observation to me that this mentality seems based in how used to "Kitchen Sink fantasy" people have gotten, which are fantasy worlds where every myth, legend, folklore, and campfire story coexist in some form or another, with superhero comics being the primary example, and thus many have the immediate instinct to assume any fantasy story they get into will be the same. While I do get how that mentality could have developed, that still doesn't really change the fact that not every fantasy story is Kitchen Sink fantasy and that you still need to let the given story tell you what its world is like rather than you just assuming what it's like. There's a difference between thinking that there are more gods of other pantheons than we're shown in Samurai Jack, which is a story that well established that it's a world with not just Japanese mythology running around but those from Greek, Norse, and Hindu as well, vs. thinking that there are more gods of other pantheons than we're shown in the original Yu-Gi-Oh manga when the only true mythological figures shown to exist in its world are those from Egyptian mythology. It may not be realistic for these gods and monsters to exist at all but that doesn't then mean that all gods and all monsters from all religions and mythologies are thus on the table.
But this isn't just a problem in regards to fantasy. Science fiction generally tries to have some degree realism and plausibility in the realm of actual science and fact, but even then liberties still often have to be taken in order to tell many stories of the genre, usually with the writers telling tales about stuff that doesn't actually exist, be it because we haven't discovered it yet or haven't found a way to create it yet. A starship travelling faster than the speed of light in order to get around the galaxy in a reasonable amount of time compared to a human lifespan is currently something that isn't realistic, but usually we can accept whatever explanation the story gives us for how it's doing it if it's based enough in plausibility and scientific theory, such as Star Trek's Warp Drive technology which creates a bubble of subspace around the ship that distorts space-time. It's technology that doesn't exist made of and powered by elements and materials that we either can't create or just simply don't exist, but the concepts work well enough with actual science and theory that we can handwave away the gray unexplained areas where the specifics make the technology unrealistic.
But if the story were to claim that the insane amount of energy needed to power this technology is being generated by a single potato and a couple of wires, that would be unrealistic to the point of being inexcusable, at least if you're still trying to claim it's science fiction and not outright magic. Yes, science tells and shows us that potatoes can generate electricity, but we also KNOW that the amount of electricity generated is relatively quite small. It can power a clock for about a day but it wouldn't be powering your house for even an hour, and thus it sure as f**k is hard to buy that it could power the physics-breaking engine of a spaceship!
This is why even in science fiction stories that play a bit fast and loose with how realistic its worlds and technology are (there's a big difference between Star Trek and Doctor Who), people still call out things like electricity being conducted through wood or magnetism being used to attract/repel things that aren't metal. Because there's unrealistic as in technology or biology or chemistry too advanced, different, and theoretical for us to say for certain that it can't exist and unrealistic as in stuff we've outright proven it can't happen the way the story is claiming it does.
And, of course, be it fantasy, science fiction, or something claiming to be the world outside your window, there's the argument that tries to use the unrealistic aspects of a story's world to excuse just flat out bad writing, usually in regards to character actions.
Yes, in Alien vs Predator Requiem and The Predator, the premise of an alien with infrared vision and glow-in-the-dark blood from a culture based around hunting is unrealistic compared to our usual reality, but that doesn't mean I thus have to just accept the main Predators of those respective movie randomly hunting, killing, and skinning a couple of humans upon landing on Earth when the first one is there specifically to stop the Predalien and the Xenomorph infestation and thus doesn't have time to waste and the second is there specifically to give humanity technology capable of fighting against Predators in a potential invasion and thus killing humans right now goes against its primary motivation! Scooby-Doo and the Reluctant Werewolf is a completely ridiculous movie but the part I don't buy isn't Count Dracula hosting a wacky race featuring all the famous monsters, it's Dracula and his Hunch Bunch doing things that would either kill Shaggy or keep him from competing in the race at all just so that Dracula doesn't have to honor his agreement to turn him back into a human if he wins the race, when the entire reason for everything Dracula had been doing up to that point was because he wanted Shaggy to be his werewolf in the race!
Just like how the existence of angels and demons doesn't mean that ghosts thus must exist since one unrealistic thing doesn't have anything to do with the other unrealistic thing, unrealistic things physically existing in the worlds of these stories doesn't then mean that the characters can thus act in whatever unrealistic ways the story says so when those actions have nothing to do with the unrealistic physical things and in fact go directly against the world and story's own established logic and premise.
Weirdly enough I think the Looney Tunes give a good example of what I'm trying to say in regards to all of this. Specifically one of their most iconic bits, "Duck season, Wabbit season." from the short "Rabbit Fire", which involves Daffy Duck demanding (three separate times) that Elmer Fudd shoot him in the face.
Now, the thing about the Looney Tunes cartoons is that they are basically worlds upon worlds where any kind of story can be told in any way that writers want to tell it as long as they find it funny, or at least think the audience will. The world and characters are completely absurd and unrealistic and thus in a Looney Tunes story anything can happen.
However, Daffy didn't demand that Elmer shoot him just because "Anything can happen and thus this thing that can technically happen happened". There was lead up to it and a logical sequence of events that, for as silly as that logic was, the audience could follow along with. Daffy didn't demand to be shot because anything can happen, Daffy demanded to be shot because that flowed naturally as something that would happen in this world with these three characters of Bugs, Daffy, and Elmer when interacting with this set-up. Technically speaking there's no reason why, say, Witch Hazel couldn't show up out of nowhere during the bit and slap Elmer on his sweet ass, since for a world and characters as unrealistic as Looney Tunes there's nothing that says that that's too unrealistic to happen, but it wouldn't fit nearly as well as everything else in the "Rabbit Fire" short did and that had an elephant showing up to punch Elmer into the ground make sense.
Anything can technically happen in a Looney Tunes cartoon because of how unrealistic its world is, but not everything that can happen fits with what the cartoon is telling and showing us that it is, thus why not just anything does happen.
And that applies to stories in general. Fiction by its very nature is something someone is making up and thus can technically be however realistic or unrealistic as they feel like making it. But it's the job of the storyteller to be consistent in whatever degree of realism they're using and likewise the job of the audience to pay attention to that consistency.
Final wrap-up:
Now, despite what everything I've said may come across as, I'm not trying to make it sound like there's no room for discussion or debate when it comes to what too realistic or unrealistic in stories. Not at all. Most stories don't exactly give the audience a list right at the start that says "This is what can exist and happen in this world and this is what can't.". We have a term called "worldbuilding" for a reason. The world and its rules, be they the tone or the physics, tend to be something that gets established over time as the story is being told, and that can cause some gray areas.
One of the most famous/infamous events in comics, the death of Gwen Stacy, serves as a pretty good example of how and why it's understandable to have those types of discussions. Even at the time this was controversial and not just because it was the death of a beloved supporting character but also for some the way she died, her neck snapping from the sudden stop of her fall off the bridge, felt too dark and too realistic for the Amazing Spider-Man series. In their eyes it didn't fit what the book had shown and told them it was up until that point, while for others it was perfectly in-line with what they felt the book had told and shown them it was. Keep in mind that this was three years after Gwen's father Captain George Stacy had been killed off after being crushed under a falling chimney. You had two different groups of people who had been reading the same story and, regardless of whether they wanted Gwen to die or not, disagreed on how in-line the realism of her death was for the story.
This especially can happen with many other long-running series and stories. Compare A Nightmare on Elm Street to Freddy's Dead: The Final Nightmare and the tones are wildly different, as are how grounded the story is and what the characters can do and survive. But the film series didn't just go right from the 1st to the 6th, there were multiple movies in-between where the changes in tone and unrealism were relatively steady and gradual and thus the more comedic world and characters felt perfectly natural to plenty of fans, to the point that when Wes Craven's New Nightmare came out there was pushback against it by some fans because despite it being much closer to the first in tone and realism it was a drastic change from what the franchise had become and what they now saw the story and Freddy as.
Or to bring things back around to the world of Avatar, there's plenty of debate regarding the technological boom that happened in between Avater The Last Airbender and Legend of Korra, at least for Republic City which served as the primary setting for the majority of the latter's seasons. For some fans, even if it makes sense that the world could now develop automobiles and power plants after so many years of the four nations coming together and pooling knowledge and resources, it's a level of realism that doesn't fit the world we'd been shown in ATLA and makes it no longer feel like that world, while for other fans it's a level of realism that's perfectly in keeping with the world of ATLA, which in the span of less of a year went from not even having hot air balloons to the Fire Nation creating an entire fleet of flying warships.
Ultimately stories are another form of art and like any form of art how it's seen and interpreted is going to vary at least somewhat from person to person, and so likewise will how realistic or unrealistic something is and how well it fits with the story they've been shown. It's why we get so many discussions around things like redemption arcs, since in some people's eyes it's completely realistic that a character would change their ways after reflecting upon themselves while for others it's completely unrealistic that anyone would change unless they were outright forced to.
What's important is to make sure that what you're debating over is in regards to what's actually in the story and not just what you're inserting into it completely on your own. It's one thing to look at a painting and say that you think the blue represents the artist's depression because of amount of blue and the intensity of the brushstrokes...it's another to say that you think the blue represents the artist's depression when the only reason there's any blue on the painting is because you threw a bucket of blue paint on it. It's one thing to debate whether something is too realistic or unrealistic for the story you've been shown because of examples you can bring up from the story that it does or doesn't fit with, it's another to declare that something is too realistic or unrealistic for the story you've been shown because "Well, it hypothetically could be the case because there's nothing to directly say it isn't." (and conveniently ignoring everything that does say that).
TL:DR: You need to let the story tell you what is or isn't realistic to happen in its world, not just insert your own beliefs unprompted from outside into the story and then get mad about them.