Having a self-selecting social group that strongly encourages both posting defensible claims and admitting when you are wrong will do wonders for a community. It requires a strong social consensus that these are desirable characteristics, of course - a sufficiently large group of trolls upvoting their own trolling and downvoting everybody else could pose a threat to the system - but that's where having the group be self-selected is a good thing.

On the other hand, I find myself forced to ask: have you any citations or evidence to support those numbers? :-D