"Sportsmanlike players have more enjoyable games"
As a player who hasn't unleashed his rage on another player for a very long time now, I can honestly say it's not true. I would be so much happier if I can verbally tear some of these fuckwits new assholes. It's more frustrating than I can express to know that they can be pricks all they want, but because I'm afraid of getting banned I can't give them what they deserve.
Edit: Just for clarity, I've never had any punishments for my behavior besides low priority queue once for 5 games, although admittedly I probably should have been punished back in the day. Nowadays I mostly say nothing the whole game aside from important info like flashes and such. I'd likely end up with a chat restriction rather than a ban if I did go off on someone, but that doesn't make taking their shit without retaliation any easier.