alt Hacker NewsTheres 3 (4?) horse men of online communities.
1 Identity topics, eg: Politics/Religion
2 Insufficient moderation
3 NSFW content
4 Inability to distinguish experienced commenters or valid content from plausible sounding content. I.E. Low Subject Expertise thresholds.
4 is what keeps a community boring, while keeping the SNR high.
I tried in vain to understand what centaur-like men had to do with your point.
"Horsemen", as in the Apocalyptic Tetrad?