Hey, my brother-in-law has been an avid rager on FPS's for a couple years now, and I asked him why he does it... Unbelievable justification of why, to say the least:
"It's natural to rage on a game where you're being violent - why can't you be violent with your words?"
... Just lol. We went on to say a bit more but that's the bottomline of it and jesus christ... What's the world coming to? XD
I've learned to accept that there are times when my mind hits a dead end. It's better to take a deep breath and step back, even if it means leaving an ongoing MP match.
You've the right to leave - not just that but the game is to entertain, you get angry, you've the right to come off
Only if it's a game like League of Legends whereas it's harshly against the rules to leave a game before its ended should you consider persisting.
But as I've said, I always try and keep my cool (which usually works) which isn't the most helpful in this situation because it's hard to empathize with Freakenstein lol (I don't want to empathize XD ).