Back up. I agree that unnecessarily harming animals is wrong. And let’s say I agree with you that I am contributing to unnecessarily harming animals. But cows, pigs, fish, and so on are here for/bred for this purpose. What’s wrong with using them?

We already recognize that certain nonhuman beings, like cats and dogs, share with us an important characteristic: they are sentient. They feel pleasure and pain, and they have interests, such as continuing to live and avoiding suffering. It is unjustifiable to harm these animals merely to satisfy our comparatively trivial interests, such as pleasure and convenience.

But it’s not just cats and dogs who have interests in continuing to live and in avoiding suffering. Other sentient animals share these same interests. Therefore, we have no justification for harming cows, pigs, chickens, turkeys, fishes, deer, or any other sentient nonhumans.