We don’t get those messages from only our parents, or we’d all behave just like our parents. Many of us didn’t end up being just like our parents, including many men who were raised to treat women like garbage. They have looked at their own behavior, listened to women (and men) who have been exploited in these kinds of relationships, and did better. The whole idea that we are set in stone at 18 is absurd, because we constantly change and grow over the course of our lives, unless we make the choice NOT to do so.
Ellis made a choice to ignore the very many counter-messages in our culture about not exploiting people who are less powerful than him, because he wanted to do so. Plus, there are enough messages in our culture, especially in comics, that reinforce and celebrate his actions, so he continued despite countermessaging.
On top of that, we are speculating about his upbringing. We have no idea about his parents. We DO see, everyday, the misogyny that exists in our culture, however. Discussing THAT can help us to change it for the better as well as send the message to people who think it makes actions like this okay to themselves do better.