I remember reading (can't think of where) where when the real civilization of the Book of Mormon period wiped out another village it was just like wiping out a heard - they saw no difference between a heard of whatever and a heard of humans.
I don't think this is true. For one thing, throughout most of Mesoamerican history they did not WIPE OUT other villages at all. War, with some exceptions, throughout most of this history was more of a raid for sacrificial victims than what we conceive of as "war" today. There was no intent to annihilate the other village, nor to "take it over". The intent was to, on the battlefield, catch enough "prisoners of war" to take back to be ritually sacrificed to appease the gods in specific, calendar controlled, ceremonies.
In an odd way, modern war is much more dehumanizing than this ancient form of war was. We really do slaughter mass numbers of human beings on the battle field. They normally didn't - plus, their elites - their leaders - were on the frontlines, and were the MOST DESIRABLE captives of all. A human sacrifice of someone with royal lineage was very pleasing to the gods. So they were at highest risk.
And the gods weren't just bloodthirsty, demanding blood for no reason. It was part of the cycle of life - human blood was their sustenance, how the gods continued to survive in their own realm of existence. They had sacrificed themselves in order to create human beings, and our debt of obligation was to "feed" them in the same way. It was a form of reciprocal altruism. And while no one wanted to be a human sacrifice, in its own way, it was an honor - to die for the gods, to repay them for giving us life itself. We now give them life with our blood.
I know that moderns look at this as barbaric - but it seems more civilized and controlled than how we conduct war today, to me. In particular, if OUR leaders were on the front lines, the most likely to DIE for the cause, I think they would be a bit more cautious about taking us into war. And the actual numbers of people who died were much smaller than today.
Although I haven't studied the Aztecs as thoroughly as I've studied the Maya, their culture is still interesting. They took the sacrifices to the extreme, in terms of numbers, and were horrifically violent in the acts. But at the same time their culture was very controlled and moral. They were very strict with their children and morals, and abhorred lying and sexual infidelity. It's an interesting contrast.
Frankly, as a religion, I think it makes as much sense as modern religions do today.