Well, that's sort of the question, isn't it?
It is. If you had asked me this in the first game I'd say he's just a careless alpha male archetype guy. In the second game some part of him seemed more malicious, which also seemed a little out of character because he never came off as menacing. Now he seems like he's not even a human or at least he's the vessel for something ancient and power that he doesn't understand. Almost like a Marvel comics Abstract or an Eldritch being that doesn't really care what happens to humans as long as it accomplishes it's mission.
Also how did Nero go through with the abortion? How is she immune to his powers and why was she so surprised when he made her cum?