It's kind of amusing the double standard Disgaea has. Murder, war and environmental destruction are okay if demons are responsible but when humans so much as pollute the air a little it's a horrible catastrophe. It's sort of like the double standard you have in regards to oni and humans. Oni using their strengths is perfectly natural and just the normal way of things, but when humans resist using theirs it's cheating. Shuten's position as I understand it isn't so much 'Being slain is just the way of things' so much as 'Well, small wonder they killed me after I hung around outside their capital snacking on people.'