Most of the posts in this thread are very selfish, and disgusting.
In response to-
But what I will say is this (even if it's a bit utilitarian without paying enough respect to other theories): The person who fills in for you is probably being harmed less than the person who sticks around. The guy who backlogs for you? He shrugs, maybe cusses "**** a losing WZ!", and then just leaves the game; because he joined the game late anyway, he feels no agency in its loss and no investment in its outcome. So he will just requeue having wasted very little time and experiencing very little frustration.
You also have to take in consideration that the next guy who joins waste a minute of his time in the queue quitting, keep in mind that if 10 more people do the exact same by joining and quiting after him in the same match, that's wasting 1 minute of 10 peoples time. Just to keep in mind.