There's no penalty for leaving an LFD group if more than 15 minutes have elapsed since you zoned in. I'm usually okay with one wipe, or even two, but if I'm in a group that's wiping over and over for stupid reasons and won't listen when I make suggestions for fixing the problem(s), I really don't think I should be forced to stay in the group, or be penalized for leaving at that point.
On the other hand, if I leave the group immediately, or in the first few minutes, I'm completely okay with having to wait an extra 15 minutes to queue again. Most likely, if I'd stayed in the group, it would have taken at least 15 minutes to finish the dungeon, so I'm not really losing any time.
What I do hate are tanks who sell "instant queues" for gold with no intention of actually running an instance and leave the moment they zone in, and DPS players who queue as tanks to get groups faster but don't actually know how to tank, don't make any effort to learn, and then roll on DPS gear.
