About 7 years ago I helped moderate a drug education/harm minimisation forum which generated about as many posts, and as varied opinions as we see here. The age distribution was similar too. For the entire time I was moderating (about 3 years), there was a lot of bickering, a few people banned, and a lot of arguments which skirted the edge of flame wars.
But amongst all the crap was a lot of very worthwhile content. And that's why I stuck around; to help make sure that content was noticed. And to try to ensure that people would try to contribute in a similarly worthwhile way, and not scare off those who really needed the information we all provided.
To that end we wrote posting guidelines, articles about internet etiquette, and maintained constant vigilance. But the most effective method was leading by example. It was clear that the most mature posters were respected by all but the dedicated trolls, and those trolls were not around for long.
The online community also formed close-knit offline social groups, all over the world. As this one no doubt will (and is starting to successfully do over here in Melbourne).
btw Logicseeker, I'm an unfaithful disbeliever, so screw you
(please note the
indicating a playful and not-at-all insulting tone)