Your beloved book was written in 1843. Prescott lived from 1796 until 1859.
No one needs to buy it now. It is on the internet because it is that old.
I have read primary sources about this topic, and secondary sources, but not early 19th century secondary sources. This book of yours is not the last word. Scholars would mainly read it now for its historiographical interest.
I do not “support” the Aztecs. What would that even mean? It is not useful to judge ancient civilizations by the standards of modern morality.
The Aztec religion involved human sacrifice, but it was not devil worship. It was just a polytheistic religion.
Cortes was not a shrinking violet. Obviously he did want to fight them.
If he was on a mission from God, then God isn’t merciful.
Catholicism as practiced by Spanish conquistadors was not a very humane or nice religion.
Prescott wrote from primary sources. And God was very mercifull to motivate Cortez to christianize the craxy aztecs and uplift their whole civilization; risking life and limb and comfort. Sorry, but morality is the same throughout history as the conscience given to man is constant. If you think mass murder of innocents in the name of a god is not demonic then you need to wake up a bit. It was all motivated by the opposite of christianity...hate. The same hate that causes murders and violence today. You can try to sugar coat the aztecs religion but it just doesn’t work.