Hm, there is already someone wanting to use their powers for evil(or, at least petty larceny), but if everyone else is more or less a good guy then that might not be too bad.  

How about we just leave it as one failed save, though?  I think that should be plenty.  Actually, I especially like the idea that it was a choice, and our hero chose wrong.  

Question, though.  What does his hatred of heroes motivate him to do once he gets his own powers?