"It's entirely pointless. Humans are vastly superior in their ability to subvert and corrupt. Even if you were able to catch regular "harmful" images humans would create a new categories of imagery which people would experience as "harmful", employ allusions, illusions, proxies, irony etc. It's endless."

This is employing a fallacy that people have infinite amounts of energy and motivation to devote to being hateful. I have been on countless online communities in video games and elsewhere and when the chat in them doesnt allow you to say toxic, hateful stuff... guess what a whole lot less of that shit is said. Are there people who get around it by changing out characters to ones that look the same that dont trigger the censor or by using slang or by mispelling? Of course but the fact is I think if you talk to someone who runs communities like this they would laugh in your face if you said a degree of censorship of hate speech wasn't fundamentally beneficial.

A big aspect has got to do with the fact that if everybody agrees to be part of a community, part of that agreement is a social contract not to use hate speech and if someone flaunts that they are bypassing it.. in the obvious flaunting of the social contract established (it is obvious they had to purposely mispell the word) these people are alienating themselves by underlining the fact that the 99% of the community finds their behavior pathetic and unacceptable.