Well, ok then. Except... in that particular case schizophrenic people usually have a poor sense of reality, heck even words like "hellban" and "dead" may have religious connotations. Not really sure what a better solution is.
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.