Victor's experience with rich people has been, for the most part, explicitly terrible. Why, then, would he not take a modicum amount of enjoyment from stealing from them? Morality is not black or white, and that is the dynamic of the duo. Cedric has seen both the good and the bad of the upper class but knows little, until recently, of the struggles of the poor. Victor is the other side of that coin. Victor isn't going to feel as bad about stealing from wealthy people who- from his perspective- faff about with piles of money to spare while people starve. Victor has been a thief for years to get by, while Cedric is just now starting. So, of course, their attitudes and emotional responses will be different.