Every time I play online, there is always a group of rage quitters out there that pretty much quit as soon as they start losing in the rankings or whatever, and in all honesty, that's exactly what I would want the opponent to do. {now if they were on my team, that's a different story.} I wouldn't imagine that he/she would take a massive ass kicking over and over again, so naturally they would rage quit as soon as they go south in an attempt to save face, which more often than not, they don't.
About the only time that rage quitting would be justified is if the opponent is constantly using cheap tactics and gang attacks on a certain player, in which there would be no reason to play, because they wouldn't be able to get into the action for very long, which would be a tremendous waste of time if they spent more time respawning or waiting in the lobby. Either you fight fair or don't fight at all, but of course not too many people will do just that because unlike rage quitting, there is no real punishment for "pwning" someone over and over again.