1- Neither the "empire", nor the slavery, nor the human sacrifices were accurate about civilizations like the Aztecs. They were mostly exaggerated and misinterpreted by Euros and later people in here to give justification to the Colonial Rule in México.

2- While there definitively was a huge spike in deaths by diseases at the beginning of the XVI century in what-would-become México (though the number is debatable), a big part of that spike in death was caused by malnutrition and overwork of the originary peoples by the spaniards.

3- The Laws of the Indies (that people justifying the spanish rule point out to to show how "kind" they were to the colonized) were supposedly made to control the worse excesses of the encomenderos (who turns out didn't have that much "kindness" in them) that didn't even work that well, since originary peoples still were enslaved and genocided if they refused to submit to colonial rule. Said laws weren't applied evenly (with one case having a rebellion against someone who should have been abolished 100 years ago) and even if they did (sort of) abolish enslavement of the originary peoples, that only meant that it was replaced by enslavement of other peoples (like africans).

TL;DR: Spanish Empire a shit, All Coloniasm is Bastardry, Burn in Hell Christopher Columbus