Argument: That animals harm/kill each other does not justify the same by humans
Michael Pollan. "An Animal's Place". The New York Times Magazine. November 10, 2002 - "My first line of defense was obvious. Animals kill one another all the time. Why treat animals more ethically than they treat one another? (Ben Franklin tried this one long before me: during a fishing trip, he wondered, 'If you eat one another, I don't see why we may not eat you.' He admits, however, that the rationale didn't occur to him until the fish were in the frying pan, smelling 'admirably well.' The advantage of being a 'reasonable creature,' Franklin remarks, is that you can find a reason for whatever you want to do.) To the 'they do it, too' defense, the animal rightist has a devastating reply: do you really want to base your morality on the natural order? Murder and rape are natural, too. Besides, humans don't need to kill other creatures in order to survive; animals do. (Though if my cat, Otis, is any guide, animals sometimes kill for sheer pleasure.)"