As a Thomist (Catholic Aristotelian), I winced when I read "their purpose is to be food". So, here's one possible counter-argument: Aristotle describes all thi

As a Thomist (Catholic Aristotelian), I winced when I read "their purpose is to be food". So, here's one possible counter-argument: Aristotle describes all things and beings as having four causes: matter (what it's made of), form (how it's organized), first cause (where it came from), and final cause (what it's meant to do). In this model, the final cause of an elephant is to live the life of a happy, well-adjusted elephant; it is not piano keys. I'm not sure what the final cause of a square is (maybe Aristotle's model only applies to that which has both matter and form), but the final cause of a living being is to live the best and most fulfilled form of that living being's life. This means that an animal's purpose can never be said to be food. Predation interferes with other beings' final causes, so it's always a material evil. Is it always a moral evil? Non-conscious beings are never moral actors, so nothing can be called morally good or morally evil for them (although it's fine to suspect that the Devil had more of a role than God in shaping the evolution of the giant roundworm); for conscious beings, when and whether predation is morally evil depends on the nature of the universe -- on which theology/cosmology is true. Catholicism, for example, teaches that humans have immortal souls and animals probably don't (although it doesn't rule out the existence of non-human intelligent life, so seared bottlenose dolphin and elephant cutlet are probably not wise meal choices); so raising animals for meat is potentially defensible -- although cruelty is bad for the human soul, and cruelty or callousness towards animals as well as towards people must be atoned for at some point. Hinduism teaches that humans, animals, and all other beings share fragments of a single immortal soul; so killing an animal for meat is pretty much the same as killing a human for meat. Jainism -- which might be the original source of Hindu and Buddhist cosmology -- takes this a step further, and similarly condemns killing plants, recommending that one should live on products that can be gathered without killing their source. Classically, this meant milk, eggs, and fruiting bodies; modern Jainism is increasingly skeptical of the idea that one can keep animals and birds without violence, and prefers eating only nonviolently-gathered products of plants. This is an unfamiliar diet -- ahimsa diets are in general -- but I doubt it would be as restrictive as it sounds; and if it's the only diet that isn't literally homicide, it would be particularly well worth following.