It wasn't ritual cannibalism. The bodies of the sacrificial victims were tossed down the pyramids and then hauled away and consumed like any other meat.
As for Gibson's movie being unnecessarily bloodthirsty one set of sacrifices for a new temple in what became Mexico City went on for 4 days with one human sacrifice about every 30 seconds day and night.
In addition you might want to look into what were known as the Rose Wars where rose screens were used after the sacrifice to screen the royalty's (both sides) feast of human. Both sides also decided how many prisoners would be captured before the battles and who would win (usually the Aztecs). These Rose Wars were on the reasons that the Spanish were able to conquer Mexico City so easily. They had lots of help from the other Meso-Americans were very happy to help the foreigners in overthrowing the blood thirsty and ruthless Aztecs. Of course the Aztecs weren't the only ones in the area that believed in human sacrifice and cannibalism (not ritual cannibalism).
The original Aztecs were landless mercenaries brought in to help when a war. After the victory the Aztecs took the daughter of the the king that had employed then and skinned her alive. They then danced in her skin in front of her father. This kind of ticked off the father and he attacked the Aztecs. Unfortunately for him the Aztecs were better warriors and they conquered the city which is now known as Mexico City. This dancing in the flayed skin of sacrificial victims didn't end there.
This isn't a real popular topic in most of the classes pushing Hispanic studies. They like to key in on the dancing, the math and the astronomy.
The Latin American History as taught by the school systems in the 1960's had the Aztec tribe as the poorest and smallest of the tribes of that part of North America. They were landless until one day while wondering through a swamp, they came upon an eagle sitting on a cactus eating a serpent (snake). This was a vision that one of their elders had dreamed of previously. They made that swamp their home and became the great tribe that the Spanish Conquered a few hundred years latter. The eagle on the cactus eating the serpent is the symbol on the Mexican Flag. There is also a book Aztec, by Gary Jennings that is a great read once you get past the sexual descriptions of meaningless fiction.
I'm glad someone got around to pointing this out, and while the film is about the Maya, efforts to portray them as terribly different from the Aztecs are more than a bit disingenuous.
It's funny how, in the U.S., the name of the ancient Roman province of Hispania has become a euphemism for "Aztec" or "Meso-American Indian" while, in Mexico itself, "Hispano" means those evil Spanish Conquistadors who put an end to the Aztec Empire.