> "Be it so. This burning of widows is your custom; prepare the funeral pile. But my nation has also a custom. When men burn women alive we hang them, and confiscate all their property. My carpenters shall therefore erect gibbets on which to hang all concerned when the widow is consumed. Let us all act according to national customs."
Sir Charles James Napier may not have earnestly bought into cultural relativism, but the sentiment he expresses is not inherently incompatible with it.
You don't need to believe that your system is "correct" in some sort of universal way. You merely need to believe that your system will be best for your personal interests.