This is a problem with message boards and the Internet in general. Ignoring that the gaming demographic isn't necessarily the most mature or reasonable group out there, the anonymity the Internet provides tends to bring out the 15 year-old in all of us in some way or another.
That said, GAF is the best gaming forum (and online community in general) I've frequented since I first started using the Internet. The rules are good quality and they're enforced by a membership policy that makes people value their accounts. While there may be a few dumbshit threads here, the proportion of shit posters on other sites is exponentially higher than on GAF.