Well, obviously, I believe we should try to quell or prevent it. Just because of temporary associations shouldn't give people a free pass at being douches (Most people wouldn't act that way to randoms, say in a bar or restaurant, without repercussions). Lack of acting simply perpetuates the matter, and leaving to join another group may not always be a viable option (after a 20 min DPS wait, I'd like to get through the dungeon and go tend to other matters). The moderation need not be very intrusive, merely a warning, an immediate (perhaps even mild) slash in rewards for that specific run, or even just the threat of it occurring would probably be enough to keep people from being douchey especially among those looking to maximize their reward with the least amount of time and effort.