A commentary of mine to a post in Cliodynamica:
A notorious example of dysfunctionality and the way it is “selected out”. The Mexican massive human sacrifices seem to have involved not only the downtrodden but also many aliens, imported slaves, captive warriors, tribute hostages from neighbouring tribes… were used as an instrument of domination by the Aztecs, and maybe did provide a measure of symbolic social unity, as a mode of “living tragedy” among other ways. But their systematic nature provoked such a degree of resentment among their neighbours (who also practised human sacrifice and cannibalism by the way) that they were more than ready to join Cortés and the Spaniard invaders in order to overthrow the Mexican empire. The ritual was functional at a given stage of development and imperial expansion, but a new player in the game disrupted the play of forces.
One has to add that the functionality of human sacrifice in this culture was complemented with cannibalism—a meat-rich diet for the warriors and the élites which no doubt helped promote their predatory efficiency on neighbouring tribes, in the peculiar Mexican ecosystem, in which humans were the only existing form of cattle and beasts of burden—yet another factor which changed with the arrival of the Spaniards.