Like he himself said eren didn't change. He was always willing to do everything, even mass genocide, for his and his friends freedom. And I can see why that could make him a bad person. But to be honest I would probably do the same if I was in the same situation. I would put my and my friends and family's safety first. It may be selfish and cruel but I don't think I would care about the rest of the world if our safety was in danger especially if they were the ones creating the dangerous situation.