The first is that, despite Gibson’s vile portrayal of the Maya as a macabre cult of deranged killers straight out of Apocalypse Now!, there is no evidence that the Mayan people ever practiced widespread human sacrifice, and they certainly didn’t target the innocent hunter-gatherers and horticulturalists Gibson chooses to portray as the victims of a Mayan death cult.
Gibson knows better. He studied the terrain in depth and had no practical limit to the funds he could expend on research. His portrayal is a conscious lie, one he uses to justify the premise that the Mayan city states collapsed because they deserved to collapse, and that they deserved to be replaced by a “superior” culture in the genocide known as the Conquest.
"A great civilization is not conquered from without until it has destroyed itself from within," is how Gibson puts it. In other words the Conquest was not genocide but a moral comeuppance; the civilization didn’t fall, in the final analysis, from climate change or inadvertent soil depletion or even war--it was conquered in god’s wrath against the forces of evil. And Gibson’s made sure you see the ancient Maya as a force of profound evil.