the concept of good vs evil to them is set up more along the lines of do what thou can shall be the whole of it. As long as their ability works, they do it. Killing to them is more of a nature based thing than anything else (think animals hunting each other); they don't have dogmas and morals attached these acts. Even though they are on top of the food chain, they don't perceive it that way because when they see humans and what humans have, such as every bit of technology (guns), they are outmatched.