People happily kill other people in the name of everything from a god to a country to an overly developed sense of annoyance when someone cuts across two lanes on a freeway without signaling. Cats will, on occasion, kill other cats but for the most part they are content to puff up their furr, yowl like banshees, and rip the occassional ear off - and all this is usually done for the sake of food or protecting their own territory (which may not be condonable but it is at least rational) .