To each their customs?
On the axis: Status of norms (metaethics) · the customs of other peoples
Peoples horrify one another with their usages, each holding its own self-evident. Does this deep disagreement prove no morality is true, or can we still judge some better than others?
This problem is brought out by the thought experiment To each their customs?:
Herodotus tells that King Darius asked some Greeks, who burned their dead, for what price they would agree to eat the bodies instead: horrified, they answered that no sum could persuade them. He then put the reverse question to some Callatians, who ate their dead: for what price would they burn them? They cried out in the same horror. Each held their own custom self-evident, and the other's a monstrosity.
Herodotus, Histories (-430)
What should we conclude from such disagreement between peoples?
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Justification
In "Of Cannibals", Montaigne turns the European's gaze back upon himself: we hold barbarous whatever departs from our usages, never seeing that our own would look just as strange from elsewhere. "Each man calls barbarism whatever is not his own practice". The diversity of customs across the world shows that our moral certainties owe less to reason than to , "other world, other laws". This relativism stays prudent, though: it serves to disarm fanaticism and cruelty, not to permit everything, for the cruelty of the conquerors is judged worse than that of the "savages".
Each man calls barbarism whatever is not his own practice.Essays, I, 31, "Of Cannibals"
Essays, I, 31, "Of Cannibals" and II, 12
Justification
The moral law holds universally for every rational being, independently of cultures and inclinations: this is the most assertive universalism in the tradition. A slight constructivist weight is warranted by autonomy: the law is not discovered in the world, reason gives it to itself.
Groundwork of the Metaphysics of Morals, section II · Critique of Practical Reason