I think I'd heard of hellbanning before, but not really registered it.

It's tempting, but in a way unfair because the hellbanned person is still posting, and not realizing they're being blanked out for everyone else until (perhaps) they leave because of the lack of response.

I don't know whether it would be better or worse to let hellbanned posters see and respond to each other's posts and comments. It's still sneaky. It would use up some system resources, but probably not very much, and it would be a public service to keep them occupied with each other.