Mesoamerican theme

It should be noted that information about the practice of human sacrifice by the Aztec (and other empires, religions, and cultures of Mesoamerican) has been relayed to scholars via the Spanish soldiers who conquered than and had a vested interest in depicting the Aztec as "primitive barbarians". That said, archeology confirms the fact that the Aztec did ritualistically sacrifice people; their own religious history records two specific incidents. 'Secular' sources of the Aztecs describe tens of thousands of sacrifices of war prisoners. Self-sacrifice (voluntary), was highly valued in many Mesoamerican religions and human sacrifice was regarded the most serious and powerful. Non-voluntary sacrifice (which actually isn't sacrifice), was not regarded. The Quetzalcóatl, a cross-culture cult, believed they had found a high form of self-sacrifice than human life. Their leaders would ritualistically harvest blood from their own bodies. As a leader, they would bear the sacrificial burden on behalf of those they had authority over. Quetzalcóatl kings and queens forbade all forms of human and even all other types of sacrifice in some cases; they instead used blood from their own genitals.
What is left of Mesoamerican culture has this to say:
"Life is because of the gods; with their sacrifice they gave us life [...]. They produce our sustenance [...] which nourishes life." - Aztec priests (long after being conquered).
"[the human sacrifice is] sent [to death] to plead for us." Or an alternate translation, "consecrated to annul all sin" -from a Hymn
"I embrace mankind...I give myself to the community." -the last words of a sacrificed warrior

According to conquers, Mesoamericans went to war just to obtain sacrifice victims. They also considered lazy or useless slaves to be acceptable for sacrifice. It is notable that the conquers do not attribute these ideas to priests. Also, confirmed Aztec records forbade using foreigners for sacrifices (in 1454 AD at least). It has been noted by scholars that if the reported numbers of Aztec sacrifices, they would have been preforming very complicated rituals to make sacrifice every 14 minutes equating to %20 of the population. This would have made them about 1302% more efficient at killing people with primitive tools than any known ritualless genocide with the advantage of modern technology. It has been suggested that the number of sacrafices was inflated as propaganda up to %6250 of the actual number. Further complicating these large numbers is the fact that Mesoamerican sources state that nobles made up the vast majority of sacrifices, followed by warriors. The large numbers would tend to suggest the nobility and army would have been eliminated rather quickly. It is known that Aztecs saved the skulls of those sacrificed and the number of skulls found do not add up to any of the reported numbers. Most of the Mesoamerican sources describing human sacrifice are pictorial rather than texts. This opens the possibility that the images were misinterpreted, not just by invaders, but later generations of Mesoamerican that made have acted on their misinterpretations and relayed them to their conquerors. The known archaeological indication of human sacrifice has been an important influence for interpreting pictorials. Some scholars suggest that the Aztec became involved in human sacrifice because politics run amok; glorification of legends and propaganda against foreign invaders turned misinformation into actual deeds; the central government of the Aztec used the phenomenon to keep their domestic enemies in check by turning them against each other and having them raid each other for sacrifices; thus eliminated nobles and warriors that were a threat to them.
All sources do agree on one aspect of the human sacrifice rituals; The heart of the still living sacrifice was removed.