Do such forums even exist?
Anyway, I know a forum with 20 000 members that has good activity and a great atmosphere. I think the laid-back attitude the mods have when it comes to banning people and enforcing the law adds to that. I mean, there aren't any forum watchmen there if you know what I mean.

You can make use of any word in the English vocabulary in your arguments (and often times you'll find words that aren't in the vocabulary at all) as long as you "try" to argue with your opponent's opinions and not his person. It's all very mature and the veteran community is great, if you ask me.
And since you could be curious, it's Mount and Blade's official forum, Taleworlds I'm talking about. The off-topic forums there are pure delight, since mainly the forum regulars frequent them, with usual noobs and retards hanging out in other, more official parts of the forums.