You say that as though the matter has been completely and definitively decided. In fact, humans often disregard that protection and hurt harmless people. Which is why moral debates are still being had, and why it's worth asking about the philosophical underpinnings of a moral position.
I suggested that Christianity offers such underpinnings. You may suggest alternate ones, but I think it would be naive to say that no such moral arguments are necessary because Nature Takes Care Of It.