I think I see why there's a problem with Derpy and not the others. You see, Derpy's a girl and Dopey, Ed, etc. are boys, and as you know girls are protected people and men are expendable and won't somepony please think of the children!
What makes me REALLY mad is that people didn't have a problem with the dwarf called Dopey. "Derpy" is the equivalent of "Dopey" those years ago. So it makes SO much sense that people have a problem with her now. Rant over. I needed to say that.