There’s a thought-provoking post on the taxonomy of good and toxic communities which is well worth a read if you care about such things. It’s about the tabletop RPG community, parts of which have been destructively dysfunctional for several years, but it does have wider application. It’s quite a long piece, but anyone trying to devise a Code of Conduct ought to read it, even if they don’t agree with everything he says.
The Troll’s Paradise is well enough documented, it’s what happens when a community has no clear rules, and the loudest and most boorish members ride roughshod over everyone else. Even a community that’s civil and self-policing much of the time will eventually encounter a bad actor or three; the Trolls’ Paradise is what happens when whatever powers-than-be in the community are unwilling or unable to do anything about their behaviour.
The Green Hell is the other failure mode. It’s what happens when a community declares it’s opposition to harassment and bullying, but in practice their definitions of such are vague and subjective, and different rules apply to members of insider cliques compared to everyone else. Accusations are cheap, it’s considered bad form or even an act of harassment itself to ask for evidence to back up any accusation, and there are no consequences for spreading malicious lies. Such communities either dissolve in infighting, or worse, become sources of poison for a wider subculture. That’s why they’re toxic.
The online community around one band I’d rather not name took on aspects of a Green Hell at one point. At least one other band’s fan community is the poster child for a Trolls’ Paradise.
Read the comments below the linked post if you want some specific context, similarly avoid those comments if you don’t want to read about another community’s dirty laundry.