I don't know if sex, booze, and drugs necessarily go hand in hand with this sort of situation, but I agree with your approximation of their reasoning. They are treated unfairly, that's for sure. They must have been livid that first year, and naturally would lash out. It's one of my pet peeves about the series that JK spends so little time talking about her "villains." Villains are so much more interesting when they are given agency.