I'm honestly more baffled by the fact that you guys are surprised by what the hero did. Yeah, he usually had some tenuous excuses for his other actions, but they were never more than that. It was absolutely obvious he was this kind of person. The only real difference this time is that he showed clear enmity towards a person who didn't seem to deserve it, while the other times he was either hostile to people who weren't paragons of virtue or simply indifferent to the life and well-being of everyone he didn't care about.
Do not forget he almost destroyed an entire continent just to get exp from a dragon. This hero is not just morally ambiguous, he is by all means evil - a clear-cut villain.