I pretty much agree with your conclusion as to why Stephen hates Django (it has little to do with him fearing the loss as power so much as it does jealously), but I disagree that Stephen is exchanging morality for being treated with the dignity of a human being. It is precisely because he’s not treated with dignity that he hates Django. If he was treated like a human (as you put it), then he would have had no need to hate Django. This is the heart of the crab-in-a-barrel mentality that drives him in this movie.
Morality has nothing to do with Stephen, because the character, as presented, is devoid of morals. We are given no reason to think he cares one whit about the people he hurts.