Are you conflating downvotes and censorship?
But, that's what moderation looks like, generally. Every social structure is moderated in some form.
Some people know they're hellbanned and post anyway.
The hellban lets that person still post and converse with people who actively seek him out, without the downsides of having tons of hate speech all over the front page of HN.
It's been said before and it'll be said again, schizophrenia is not a catch-all excuse for someone in a public forum.