We have canine teeth, aren't we designed to eat meat?
Short answer: Gorillas and hippos have huge canines and eat plants. And being able to eat meat was never the same as being justified in it.
Relative canine size (illustrative). The biggest canines belong to dedicated plant-eaters, they're for display and combat, not catching prey.
The Open University, OpenLearn
The objection
“Humans have canine teeth, the pointed teeth that evolved for tearing flesh. If nature gave us the tools of a meat-eater, surely using them is natural and appropriate.”
The answer
Start with the teeth. Human canines are short, blunt, and barely project beyond the rest of the tooth row, nothing like the long curved blades of an actual carnivore. More tellingly, big canines are common among dedicated plant-eaters. The gorilla, an almost exclusive herbivore, has enormous canines. The hippopotamus, a grazer, has some of the largest canine teeth of any land mammal. The male musk deer bears sabre-like tusks. In these animals canines are for display, threat and combat over mates, not for catching prey [1]. The very feature offered as proof of meat-eating shows up, in far more dramatic form, in animals that eat none at all. Canine size tracks social competition, not diet.
Concede the anatomy entirely and a deeper problem remains. Being capable of something is not the same as being justified in doing it. Our hands are capable of violence; that doesn’t make violence permissible. We constantly use reason to override what our bodies could do, precisely because we can weigh the consequences for others.
And the decisive fact sits on our plates rather than in our mouths. Major dietetic bodies confirm we can be fully nourished without animal products [2], which makes the killing a preference and not a biological necessity. The argument was never really about teeth. If someone were born with unusually large canines, we wouldn’t conclude they were entitled to harm others. What we may do has never depended on the shape of our teeth.