I very, very seldom ragequit in MP. In SP, sure, it has to be fun. But in MP, it's very rare for me to quit just beause I'm having a hard time.
Hardships are challenges. Am I getting my ass handed to me by the other team? Well, it might suck, but it's a challenge. Is my team a bunch of idiots, that has no concept for the game and it's mechanics? Then I'll have to see how much I can do on my own.
There are many a time where MP sucks, especially on the consoles. But there's nothing more frustrating than having a game end prematurely, just because someone couldn't endure for the 5 minutes it takes to finnish the match. You can't own 24/7. There are people out there who are better than you, and people who are worse. You should learn from the first group, and pass on to the latter. Ragequitting helps noone.