Custom and the judgment of barbarism: does 'Of Cannibals' teach that all customs are equal, or that a natural standard survives to convict European cruelty?

Michel de Montaigne, answered from the texts and cited to the page.

The position in brief

We call barbarous whatever is not our own practice; that is the first thing to see, and the hardest, because custom sits so deep in us that we mistake it for nature and reason. The people of the New World, whom we call savages, roast and eat their dead enemies — and we shudder, and count ourselves civilized. Yet I find more barbarity in eating a man alive than in eating him dead, in tearing by racks and torments a body still full of feeling, roasting him by degrees, and mangling him with dogs and swine — as we have not only read but seen within fresh memory, and not among old enemies but among neighbours and fellow citizens, and, what is worse, under the pretext of piety and religion.

So the lesson is not that all customs are equal and judgment impossible. That would be its own dogmatism, and it is not what I wrote. The lesson is double: first, humility — strip away the presumption that our custom is the measure of civilization; and second, a standard survives the stripping. There is a nature, a plain and frugal condition, against which cruelty is cruelty whoever commits it, and by that standard the Europeans who burn men for their faith are the deeper barbarians. Relativism about custom, yes; relativism about cruelty, no.¹²³⁴

Sources

I am not sorry that we should here take notice of the barbarous horror of so cruel an action, but that, seeing so clearly into their faults, we should be so blind to our own.
The Essays, Complete
The nature that would eat rhubarb like buttered turnips, would frustrate the use and virtue of it; it must be something to trouble and disturb the stomach, that must purge and cure it; and here the common rule, that things are cured by their contraries, fails; for in this one ill is cured by another.
The Essays, Complete
For this is the utmost point to which cruelty can arrive: "Ut homo hominem, non iratus, non timens, tantum spectaturus, occidat." ["That a man should kill a man, not being angry, not in fear, only for the sake of the spectacle."--Seneca, Ep., 90.] For my own part, I cannot without grief see so much as an innocent beast pursued and killed that has no defence, and from which we have received no offence at all; and…
The Essays, Complete
Those that paint these people dying after this manner, represent the prisoner spitting in the faces of his executioners and making wry mouths at them. And 'tis most certain, that to the very last gasp, they never cease to brave and defy them both in word and gesture.
The Essays, Complete

Where the argument is made

The Essays I.31 ('Of Cannibals', on the Tupinambá of Brazil, 'each man calls barbarism whatever is not his own practice', and the comparison of New World warfare with European torture)
I.23 ('Of Custom, and that we should not easily change a received law', the deep power of custom over judgment)
III.6 ('Of Coaches', on the conquest of the New World and its cruelties)
II.11 ('Of Cruelty')

How the argument was received

"Of Cannibals" is one of the founding texts of the European critique of colonialism and is routinely read as an origin of cultural relativism and of the "noble savage" that Rousseau would develop. The interpretive contest is precisely whether Montaigne is a thoroughgoing relativist (all judgment is custom-bound; no culture can judge another) or whether he retains a natural standard (the appeal to "nature" and the ranking of live torture as worse than cannibalism imply a cross-cultural measure). Claude Lévi-Strauss claimed him for structural anthropology; the postcolonial reception is divided between celebrating the anti-colonial critique and noting its idealization of the Tupinambá. The essay's placement during the French wars of religion gives the comparison with European cruelty its edge.