Yeah, thats how i see it too. I PuG'd a lot in Cata and many times it was over when someone left. Everyone of them traitors ended up into our blacklist, which was kept in the guild forum. When we were doing our weekly alt runs and someone from the List whispered, i told that they can find someone else's raid to leave, we don't want you.
Oh well, at least we got the laughs in the Vent because some of them started to rage and many screenshots got shared.