The Buddha ate meat, permitted monastics to eat it, and explicitly refused Devadatta's demand to make vegetarianism compulsory — the rule he set instead was the threefold one: a monastic may not eat flesh they have seen, heard, or reasonably suspect was killed for them. The logic is about complicity in the intention, not about the meat. Mahayana sutras later rejected this outright, and East Asian monasticism has been strictly vegetarian for over a millennium; Tibetan and much Theravada practice is not, for reasons that are partly agricultural — very little grows at four thousand metres. The modern argument is that the threefold rule was written for a world where you could tell, and a supermarket is not that world.