Meself, that's were the study comes in. What is universal and what is local mores? Spartan youth had to steal their food and eventually kill a peasant/slave. The Papacy burned quite a few Gnostic "Perfects" alive following the fall of Monserrat -- and not to even get into the Inquisition.

I don't pretend to know The Universals, but I'd guess at some of them, recognizing that circumstances can alter the ethics of the act. E.g.:

Don't kill anyone unless you have to.
Tell the truth whenever possible.
Try not to hurt anyone unnecessarily.

He is a barbarian, and thinks that the customs of his tribe and island are the laws of nature.
                                  -- G. B. Shaw