How do vegetarians and vegans justify buying pet food? You can force your diet on your kids; a dog can even be relatively healthy on a vegetarian diet, but your cat will die if it doesn't eat meat. What's the difference between supporting the wholesale slaughter of animals for human consumption and supporting it for pet consumption?
I knew some people once who didn't feed their cat at all. It had to survive on what it could catch itself, and it was the biggest, strongest cat I have ever seen. The damn thing had pecs. Not very friendly though... and I bet it killed a bunch of native birds along with all the mice and rats.