I don't think ANYONE would call a lion killing a cub "murder". That's how we know there is no "universal moral rule against murder". There is a rule among humans and some other social animals, but that's to ensure their survival.
We will have to agree to disagree.
You and the New Atheists seem to think the
self-interest and self-preservation of mutually advantageous cooperation defines morality.
The traditional morality of religion and ancient philosophy is that people are obligated to try to live lives of
utterly self-denying disinterested benevolence towards others, including strangers and even rivals. It's not about utility, self-preservation through cooperation, or the expectation of reciprocity.
I'm still waiting for you to tell me who first figured out murder was wrong. And what was the reason they gave for why murder was wrong?
Religions like Judaism, Christianity, Islam, Gnostics teach that humans are made in the image of God, and therefore have an
innate value and dignity, and we are made for a purpose - which is to love and respect each other.
We are not just biochemical collections of matter and energy.
Therefore, murder is a diabolical violation of humanity and human purpose in these worldviews.
Murder was certainly widely practiced in Bronze Age civilization, for example ritual human sacrifice, abandoning female babies, Exposing weak babies