Pet Peeve: Spontaneous Morality
Some settings have some very common moral criticisms.
To the point where any random Average Joe that enters the setting is pretty much obligated to comment on some genre issue.
This is usually pretty annoying because the author isn't actually writing a story about some moral conflict, they just feel like they have to include it.
So the Average Joe will look at Batman and Robin and make some comment about child endangerment, and Batman will make some excuse that he'd fight crime with or without Batman so it's better to be there.
Then Average Joe will sneer at that, but not make any counterargument and they will be pissy at each other for the entire story.
There will never be a resolution or character development because the author is absolutely not going to go into that debate, and it's just generally obnoxious and brings down the tone.
That's bad enough, but then they do it with crossovers.
With characters that do the exact same thing.
Naruto Ninjas and Robins absolutely do not have much to say about age.
Methodology, or training, plenty of other issues, but not age.
Not only have I seen this, I've seen stories where it goes both ways.
Whichever side the author is biased towards apparently spontaneously develops this moral standard.
It comes across as completely artificial and stilted.
None of them have the background morality that would lead up to this conclusion, so they just seem to bleat it out without any context or nuance at all.
And then the author doesn't do anything with it because it's not a story about morality!
Some common moral points of contention:
Child abandonment/neglect/endangerment
Lots of stories have young characters, and lots of them have almost no adults and lots of them are perfectly fine with that.
Trying to tack this on later requires a lot of world-building and excuses.
Killing/violence/torture
This can be tricky because a bunch of settings seem to have a lot of killing happening off-screen, with a lot of ambiguity over whether the antagonists die, or survive, or if the MC realizes they died and there isn't any clear moral stance taken.
It can lead to some weird scenarios where the character from the hellish death world is protesting the violence of a setting that's much lighter overall, but shows more violence on-screen.
Slaves/Clones/AI labor
This one is sneaky because some settings have this out and obvious, but others will seem to avoid it... except for that one filler episode where they totally had it and were completely fine with it.
There's so many ways it can be implemented that you end up saying "Wait a minute, that artificially created golem is totally an enslaved AI just like the one we're talking about!"
Mind control
Very common in Masquerade settings, very uncommon to be used by the MC themselves.
Makes for a lot of objection despite the fact that they implicitly benefit from it all the time at home.