YOu have to understand, online gaming is different from most other forms of gaming. When you're playing with friends, you all know each other: any trash talk is all in fun and you all have a good time playing. If you play with people who are actually professional about it and love the competition and sport of the game, then most people tend to have respect, sportsmanship, and an at least decent sense of teamwork.
But online play allows for anyone and everyone to play together. Meaning that all the immature douchebags with serious issues, God complexes, and vulgarity disorders play in the same place that the serious players do. It's unfortunate, and there's not much that can be done to stop it.
But I think the game that's come closest is Halo 3, with it's MLG playlists. It has the rules of the Major League Gaming, so pros are attracted to it and noobs stay away. It's very nice, actually: now to add a similar mode to Gears of War 2, where melee does much less damage and chainsaw kills aren't worth as much as real kills...