We have canine teeth for eating meat
Tooth shape is a weak guide to diet. Gorillas have far larger canines than humans and eat almost entirely plants.
Our bodies carry the record of how our ancestors lived, and our teeth are part of that record: we have canines alongside our grinding molars because humans evolved eating meat as well as plants. Eating animals is not a cultural accident or a moral lapse but something our anatomy was shaped for, and a diet that rejects it entirely asks us to live against our own biology.
Human canines are small, blunt and barely project beyond the tooth row. Across primates, canine size tracks social display and male-male competition considerably more closely than it tracks diet: gorillas and baboons have formidable canines on largely plant-based diets, while the teeth of actual carnivores are blade-like and set in jaws that move only vertically.
Our molars are flat and grinding, our jaw moves laterally, and our digestive tract is intermediate rather than specialised in either direction. Comparative anatomy places humans as generalists, which is consistent with the archaeological record. None of this addresses the ethical question, which concerns what we ought to do now that the choice exists.
Treating 'natural' as evidence of 'good', or 'unnatural' as evidence of 'bad'. Whether something occurs in nature tells you nothing about whether it is beneficial or right: hemlock, malaria and infant mortality are all perfectly natural.
How it applies here: Presents an anatomical fact as a justification, as though what our bodies can process determined what we are entitled to do.
Moving from a description of how things are to a claim about how they ought to be, without supplying the moral premise that would connect the two. Identified by David Hume.
How it applies here: Even granting the anatomy in full, nothing follows about what we ought to eat without a premise connecting physical capacity to moral permission.