America has a cultural monopoly on most of the media produced these days, a notable exception being animation, where anime is competitive with the West in terms of popularity. While most people seem to be ambivalent about anime online, it does have its dedicated base of haters and toadies.
Some of the hate is just contrarianism, but there are some people who legitimately don’t like it. Most of these criticisms boil down to:
Fanservice: personally I don’t mind it, but the techniques that are used to make fans horny can get old quickly. It’s definitely too common, but most of the puchback (particularly from men) seems performative.
Art looks too weird: on average, anime converges to a certain aesthetic, but there is definitely a lot of variance in art styles between anime that viewers aren’t aware of. This is especially true if they haven’t watched the more underground stuff like Tatami Galaxy, Kaiji, Kaiba, or Monster. That said, a subjective dislike of the “common anime artstyle” is a legitimate reason to dodge/dislike anime.
It’s for kids: this is a perception that originates from ignorance. A lot of anime are clearly not meant for children — notably Cowboy Bebop, Blue Gender, Gankutsuo, and Serial Experiments Lain.
It’s immature: I guess you could say this is a steelmanned version of the earlier complaint. I don’t have data on this, but I would guess that the average anime series is more “immature” than your average Western television series, and so are the fans. Regardless, it is easy to tell which anime are “mature” and “immature” before you start watching them. It’s really just a skill issue.
The fans suck: this is definitely true, especially in the modern age. Because most modern anime is bad, it isn’t particularly surprising that a bad show has bad fans. This is an individually-dependent kind of thing; I personally don’t care.
It’s low status: nobody actually says this out loud, but it is definitely true, and a lot of these earlier criticisms are probably just excuses to not like it due to this.
There is also another big reason: it is not as good as Western/live action TV.
But with an aside: variance in anime quality is higher than variance in quality in other mediums.
Western television is far more constrained by budget and technicalities — it costs less money to make Legend of the Galactic Heroes into an anime than a live action series; the opposite is the case for normal romcom stuff. Because of that, you see a lot more scifi or fantasy anime in comparison to live action series, which tend to be dramas or comedies.
The lower barrier of entry leads to lower levels of baseline quality due to selection, but does not affect the right tail as much; in fact, a lot of otherwise good stuff that could not become live action series can become animated series, so the right tail is inflated.
As such, the top tier anime is competitive with the top tier of live action.
Or arguably better. But I haven’t watched enough traditional Western TV to make that judgement.
I hate the Zogslop trend of having the protagonist who's killed niggas not know what sex is/be afraid of women.
90% of everything is garbage, this isn't unique to anime since it applies to all genres and mediums.