Aztec Human Sacrifices
Human sacrifice was relatively common among Mesoamerican peoples prior to the arrival of European forces; it was not considered particularly shocking at all. In fact, for the Aztecs and others, it was a rather ordinary part of the cycle of the religious year, something essential to maintain balance with the gods and to maintain their favor.
Amongst the Aztecs, sacrifice can be broadly divided into two categories. The Aztecs sacrificed some of their own people; this was considered a highly honorable death, much like dying in battle for a man or childbirth for a woman, and resulted in an afterlife in paradise with the gods. It is likely that Aztecs sacrificed to their gods went relatively willingly, and without any significant fuss or complaint.
While these sacrifices came from all social classes and age groups, many were, according to reports from Spanish conquistadors, from the upper classes, including the wealthy and noble. This was a social norm for the Aztecs, and for many other Mesoamerican groups. When you place human sacrifice within this context, giving someone of higher value, rather than lower value, is a logical choice to appease the gods.
The Aztecs also quite regularly sacrificed captured enemy warriors; in some cases, the enemies were largely fictional. Cities would agree to mock wars with one another to capture willing sacrifices from each side, for instance. In other cases, the enemy was captured in battle and sacrificed to the Aztec god of war. One can only assume this was likely a much less willing process.
Typically, the Aztec sacrificial ritual placed the victim upon a stone altar. An obsidian knife was used to penetrate the chest, and the heart, still beating, was removed from the victim. The bodies were rolled down the steps of the pyramid upon which the altar stood, dismembered, butchered, and cooked and served to the nobility.