Source?
While it's true they killed a lot, like most empires 5 centuries ago, they weren't as bad as the others.
Hernan Cortes defeated the whole Aztek Empire with 600 men. How? Easy, he had multiple tribes helping him because almost everyone of them wanted the azteks gone. That means they waged war against natives and they won. It has nothing to do with sacrifices.
From a total population of around 45 million, around 95% of them died smallpox and other deadly viruses.
Cortes even married an indigenous woman and had children with her just as a lot of other conquistadores did. The Catholic Kings legalized and promoted mixed marriages almost 500 years before it was legal in the US. That's why from Argetina to Mexico you can find millions of natives, millions of mixed people and millions of europeans.