Googly has already expressed my opinion on this matter.
Lets take this scenario for example:
You are playing football (soccer for you yanks) with a bunch of strangers. Everyone is playing fairly and having a good time, but suddenly a new player comes along. This player plays the way he wants to, but within the "rules". He pushes people, does sliding tackles in a violent fashion and generally abuses the rules as much as possible. On top of that he yells profanity at his opponents when they lose and curses them when they score.
As fair player, you can do 2 things about such a guy:
1) Adopt his playstyle because it evens things out, or
2) Take the opposite stance towards that players, abolish such play and advise him to play "properly". That includes leaving him out of future games because no one wants to play with him.
For a moment, let's be real folks, in real life what would you do against such a "team player"?
For the people who say: "Nuuu-huh, i play on the net so i can do whatever i want without fear of vengeance (gettin' beat up in real life for such a behaviour), well you people need to grow up, get some balls and participate in society the proper way.
You can play games (computer or not) in many ways, but it's for certain that one of the ways doesn't get you invited to cool parties.
You're playing with other people here folks, be nice, be fair and do what you'd do in real life.