I do not know if it´s really that surreal and unrealistic.
I mean, the entire Inca´s religious beliefs were based on human sacrifices of the lower caste. They even have the Capacocha, where even noble families sacrifice his children because they were the best and pure.
The Karankawa and the Aztecs were known to practice cannibalism: warriors would eat a strip of flesh from enemies they had slain in combat. That was a symbol of status.
I'm just going to ignore these particular examples, since I just don't know enough about these cultures, but...
It´s not so strange the existence of entire civilizations that has "evil" practices that are tolerated and even encouraged by their society or social group in the real world.
It would be weird if there is not in a fantasy world.
You do not even have to search much about their motivations: The ethical and moral values of their society are what could be considered "Evil" by the standards of most other communities.
The Drow are much closer to what you describe as an evil society, however, I have an issue even with that, because I have a hard time seeing a society built on making everyone as miserable as possible survive long term without frequent revolutions, without everyone being inherently evil and predisposed to violence.
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As stated before, the Actecs, Incas, Celts, Karankawa, the Huns, the Mongols... even the Vikings or the Roman empire (Wich was built on conquest, pillage and slavery, but they were very good at assimilating cultures, public works and bureaucracy) beg to differ.
They simply focus their violence on other cultures or countries or slaves so those empires last for a long time.
You have a hard time believe it because you simply disregarded the examples of long-lasting societies that uphold behaviour that is considered "evil" in modern standards, as you said before.
And of course, there are people inside a society that do not comply to the standards, but the majority do not see it as awful because it´s not bad behaviour in his society to treat slaves or minorities as possessions, easily discarded, for example.
And if that happened in the real world in ancient times, why not in a (more or less) medieval fantasy setting?
...using the word ignore was a mistake in my previous post, let's pretend I didn't.
The problem with using those societies as LOOK AT THEM, THEY WERE EVIL is that we have few to none primary sources on those. It's why I decided to focus on the Nazis in my previous post. From all of those, knowing most about vikings, let's look at those a bit (but only a little bit, since my actual knowledge is very surface level)
Most accounts of these societies we have are from opposing cultures who had everything to gain from villainising them. English for Vikings, Romans for Celts, Chinese for Mongols, Spaniards for the South American societies. As for vikings, calling it a 'viking culture' is a misnomer, since viking was a thing to do, a job. Most old Danes, Norse, Swedes, etc. were mostly farmers and traders, much like other cultures of their time in Europe. Viking was happening because they were trying to find a better place to live, since the Scandinavian peninsula is not the most hospitable place to live.
But because unlike the English and the French, they didn't keep a whole lot of written records, the modern perception of them is twisted, since the English and the French did keep records, encountered all 3 groups of the Scandinavian societies (vikings/raiders, traders, farmers), and because they really did not want them there, mostly focused on the 'violent brutes' part when talking about them, to justify fighting to drive them away. So ultimately, I pretty much disagree with the notion that there were 'evil' (evil is such a loaded word too) societies. Societies with some harmful traditions, habits, or bad leaders? Definitely. Most societies fall under that. But none of them were evil.
Same (or close enough) applies to the other societies you mentioned.
Well, except for Romans, but outside of their imperialist desires, and occasional nutty ceasar, I don't see why are you calling them evil.
