I've even seen a number of subreddits with no moderators/inactive moderators which were pretty good, even with a few thousand members.
I suppose might be that the forums you're discussing may be one of the ones created with the express selling point of having low/no moderation, while these other places where created as a place to have discussions first and foremost.
But I had the impression that you habe to ignore a swath of racism, sexism, homo/transphobia, and conspiracy theory to find them.