I don’t believe they actually believed it was necessary. I think it’s more likely that the people in charge knew it was a powerful tool to compel compliance. Just another variation of a fear society as Mayan Scharanski would have described it.
The mass murderer was a tool, not a belief. The Conquistadors rolling into those places is analogous to the Allied armies rolling into Nazi death camps. Thank God the societies were wiped out. Conquistadors were Heroes
Yes, the Conquistadores encountered horrific primitive pagan slaughter that came from a time before Christ’s birth, not with any Classicist mythology known to the European world, but from a much darker place far removed in time from the developed world of their time.
The encounter of this Christian civilization, with colonial and monarchical structure supporting it, with the primitive fear based paganistic monstrous hierarchic tribal prehistoric had to have been beyond either’s comprehension. And Christianity (nevermind what the regressives push) was clearly superior.
Your analogy of Allies rolling into Nazi death camps is a good one. For at it’s deepest psychoses— the Teutonic Pagan Runic Cult of Aryan superiority which was contrived and “researched” and “confirmed” by Himmler- was the “State as Religion” guide that blessed the horrific mass murdering of all who opposed the Pagans. C.S. Lewis and JRR Tolkein both addressed this as pure evil when the pagan god Satan ruled mortal man for a time- and no greater proof of the presence of evil and that good can and should triumph.