Seeing as people have been self-moderating some of these forums for more than 20 years, it's a solved, non-issue. Just because you're not familiar with this, doesn't mean it doesn't work. It's worked since the 70s with bulletin board systems.
My forum mods loved the power they had as well seemed to work well. The real problem is money. Forums cost time and money to administer, Reddit is “free”. Those of us that ran the forums grew up and have better shit to do and spend money on
Yes, those required moderation too.
Again, solved problem for community sites.