Good moderation can keep out bad actors and promote an adult and civil tone, but it's insanely time-consuming and expensive.
There really needs to be a new legal concept - something like poisoning of free speech. It's one thing to have unpopular and unusual opinions and to argue them, but another to set out to knowingly and deliberately subvert and poison communities with calibrated lies and aggression.
There is no upside to the latter, and the face-to-face equivalent would usually have consequences. Free speech advocates online seem to believe that online communities are somehow magically strong enough to handle these threats automatically - but in reality they can be more fragile than face to face communities. Some formal appreciation of that might not be a bad thing.
one of the few cases where online and offline worlds converge on a common modality to deal with common fundamental inputs. you don't know the valence of a new group member until they choose to reveal it to you, when it most favors their leverage.. This (among other things) tilts the odds of successful group influence in the favor of the new comers. Freedom isn't free and all that.
Part of the problem is that online communities rely on the fallacy that, because most people are good, such communities can thrive with some reasonable amount of guidance. But it only takes a relative few people acting in bad faith to cause great damage.
As such, I've long considered that the online world amplifies the sociopaths, bad actors, and worst among us to an untenable level, giving them outsized power and voice. I think it's driving our "real" society and culture in a negative direction to a degree that people vastly underappreciate.
Layer on top of that adversarial nations that actively use our online communities to divide and propagandize, and there's a very real question of whether we're better off without these communities.
More succinctly, many of the largest platforms that enable online communities seem consistently unable or unwilling to rein them in. And when you look at experiences like those you convey, it's little wonder. Attempts to moderate bad actors will invariably add to the problem, as they devolve the discourse further and generally seek to be heard, else burn the place down.