While Maou has her reason to do what she does, but she actually unite with her race's enemy to hit her own kind for her personal gain (I think it touch on briefly that the demon world is not an absolute monarchy, and she has no direct control over other powerful demon lords. If the war against human ended the demon lord will fight against each other, so maybe they will fight her tribe too, and her tribe is not known for battle prowness). In history we have Brutus, Benedict Arnold and Wang JingWei, all are considered classic traitors despite all of them have their own reasons. What makes Maou different?
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They came first for sharks fin,I didn't speak up because I don't eat sharks fin.
Then they came for foie gras,I didn't speak up because I don't eat foie gras.
Then they came for Toro (bluefin tuna) sushi,I didn't speak up because I don't eat sushi.
Then they came for me and force me to be a vegan by that time no one was left to speak up.