There's no difference between a Minecraft server implementing moderation policies and an MMO implementing them. The self-moderation we're talking about would be on an individual level.
"People doing their own moderation" includes a community of people who get together, appoint moderators, and enforce their own rules.
The people appointing moderators are part of the central entity, unless you mean that the trolls being muted also have a say in it. Show me one such server that is not a tiny one with just a bunch of friends, where moderation is not needed anyway.