I had to unsubscribe from sci.electronics.design; the s**posting over politics out-massed the electronics design discussion 100:1 (and wasn't even entertaining, just the same 3 people blowing each other up).
Thus nobody new joined the groups and they stagnated.
I quit Usenet 20 years ago and if I look at them now some of those same trolls are still around. Or they have migrated to facebook/twitter.
“Moderation” can be implemented by a cohort of likeminded people by sharing and maintaining a kill file, similar to how mods on a subreddit determine who to ban. But they only are effectively “banned” for the people to trust that cohort and agree with their decisions enough to “subscribe” to their kill file. Don’t like that they banned too many people you want to hear from? Fork their kill file, or subscribe to a different cohort’s kill file.
Make the UX good enough and it may be possible to satisfy the “free speech” absolutists as well as the people who want a well-moderated platform without trolls.
But like I said the problem was the new people. They'd open up the group see 90% junk and not bother going any further.
This is extremely demoralizing.
Even in things like Facebook groups which largely replaced the forums I used to be on.
The lower barrier to entry, and the larger and more diverse audience mean for some of these facebook groups, the mods actually tell members to knock it off.
So then those folks create a separate chat for the shitposting mixed with the original content.
Just what I have seen anyways. A few forums manage to be quite prolific still (like the BoingBoing bbs).