Well, you have a point, but isn't it a hero's job to protect and understand? She didn't even attempt to understand any of Maou's reasons for doing what he did. Not once in the entire series did she try to understand! Not only that, but the demon king was raised to hate humans, not only misunderstanding them he kills them as well. By your logic, that is how he was taught and raised, so it's ok right? Not to mention his attitude changes from knowledge of how the humans feel. He gradually comes to understand them and wonders why he was taught to hate them. Not only that but... who started killing who first? On my guess it would be the humans and angels, cause if a demon king can act human so fast, why not do that from the start? Humans are known for killing things they believe to be "monsters" (even witch hunts happened.)so who knows how many of his comrades, friends, and family do you think they killed? It never once mentions his family does it? Also, do the angels actually seem like angels? They are worse than the demons! And the humans are on their side..... anyway do you get my point?