I was thinking about this the other night actually.
Youtube is one of the biggest online communities, and seems to have little to no official moderation. What you get is a load of rubbish commentary, racism, arguing, bullshit claims, and general online disinhibition effect.
You then look at smaller communities like this one, with strict moderation, and you see (mostly) civilised conversation, discussions about different views, and general learning, guided by a primary interest.
Obviously these are very brief summarys, but I think there's an interesting study to be made here-maybe this is reminiscent of the real world? Maybe an overly strict government, that at least appears to be working in the direction of the people works best.. hmm?