I think self-moderated threads are, almost by definition, censorship. But then again, when a moderator deletes your post, that's also a form of censorship--but I would not argue that either one is wrong. I think the forum needs more of this kind of censorship, because usually what's being deleted are either posts that break the rules or ones that are of little value and just distract from the better posts.
When someone shows their shitposts around, there is no reason to keep their shitshows upfront, forever. For those cases, censorship is essential thing to do.
Another point is, most of self-moderated threads (from good OPs, not scammers, I meant) clearly emphasize that those threads are self-moderated, with some
local rules. Posters who violate those local rules will see their shitposts deleted. I think it is transparently, and fair enough.
You also mentioned about local rules
The only reason I'd asked cryptohunter and his gang not to post in my thread was because I didn't want any trolling posts there, and I'd heard everything I needed to hear from them. The thread would have devolved into a flame war.