Basically agreeing with most sentiments expressed here; when you queue for a roulette, you accept that you may be put into ANY of the content that roulette contains. If you don't like that, don't queue for the roulette. It's as simple as that. If you leave because you don't like what you got...
EDIT: As has been pointed out, it is somewhat hipocritical to impose my morality on other players. While the ideal behavior is definitely to queue with expectation that you could get a crappy run in a crappy instance, and to finish anyway, do whatever you want. Just know that there are a lot of people in the community, myself included, who find that sort of behavior deplorable.