Subreddits are pretty heavily moderated via the "report" buttons. Moderators are basically whatever community member created the community plus the other volunteer users that they picked, and if you have a problem with a subreddit's moderation the usual response is "It's my sub, you can leave."
Reddit recently deleted a whole bunch of subreddits because they decided that wasn’t good enough.
Anecdotally, I know someone who was interested in one of those topics (zoophilia), who thought the subreddit in question was “a dumpster fire” yet was still upset about it being banned.
I'm not sure how that would work for facebook.