I'm always down for some proper interstellar warfare. Author can put every single cliche into this manga as long as the warships look cool I'll be happy.
Not putting our modern standards of morality on different cultures is for studying ancient cultures, not dealing with a modern society that normalizes child gore porn.
I don't think it's that bad but the real issue is that he just lets them go without any consequences. He has an island in the middle of nowhere surely it can't be that hard to make a prison for them?