Pythagoras was pretty wild, being a very early proto-vegan.

As long as Man continues to be the ruthless destroyer of lower living beings, he will never know health or peace. For as long as men massacre animals, they will kill each other. Indeed, he who sows the seed of murder and pain cannot reap joy and love.

It was complicated, to be clear (hence “proto-vegan"), but that kind of statement today would be controversial.