I don't necessarily buy into the whole "maya/azteca" human sacrifice thing.. I think it is a gross exageration on the part of anglo/western/spanish sources..
after all, imagine you walked into a Catholic/Orthodox church hundreds of years after they are abandoned and left in ruin, and you have to construct a scenario to their use and the people who used them based upon a few bits of evidence and what you see.. well shit, you might hear people saying things like, "Drinking Jesus blood and eating His flesh" and all the graphic imagery of crucified Jesus icons and statutes.. shit you might speculate that they actually killed someone every sunday if you didn't know any better..
essentially I believe the 'sacrifices' of the meso-americans were like the sacrifices in a catholic church, they were spiritual, symbolic. I do not trust the word of spaniards from the 16th century, and there is not much factual evidence aside from their written accounts..