You can't remove rudeness from human nature. Some people are just born arrogant, hateful, and downright nasty. However...
When a game has a nearly uniform skill curve (and low skill ceiling), people trying to be competitive get more frustrated. When so much of a game is based on outside factors, this frustration naturally gets directed outwards. This is why your average console game has communities way worse than your average PC game.
If I lose a gunfight in COD, it's almost always out of my control. I may react insanely fast and not miss any of my shots, but still get killed. That's frustrating because there's nothing I could have done. When something doesn't go my way in SC2, it's either because my opponent did a smart move that I didn't anticipate or because I made a mistake. That's still frustrating, but I'm frustrated with myself - not with the game. With the former, you get mad. With the latter, you tip your hat to your opponent and try to get better for next time.