In fact, upon further thought, if this weren't the case it would probably warrant changing the alignment entry for humans to "often evil" or maybe even "usually evil".
Premodern human societies were basically like Drow society: sustained entirely by the power of Evil. Only instead of supernatural evil from another world, these societies were sustained by the homespun evils of slavery/serfdom, child labor, a rigid class system, and draconian punishments that everyone bought into.
Couple things:
Premodern human societies had evils in them, but were not evil by their nature. Slavery -sucked- in Rome. But slavery in that era was -way- different from the chattel slavery that came much later. To the point where slaves had rights. RIGHTS. Ain't that crazy?
In fact in Carthage slaves had -explicit rights- to walk away from their Master's holdings, find a guard, and ask for sanctuary if their master was cruel. Granted, cruelty was a high bar for the slave to prove. But if the slave could, with the help of the court and his fellow slaves, prove that his master was particularly cruel he could choose a kinder master for himself. As could -all- of the other slaves owned by that master, essentially ruining that dude for being cruel.
This gave slave-owners an explicit reason to be well known among slaves as particularly or exceedingly kind to their slaves and slaves in general, since slaves were a valuable property and it meant that if someone else was a jerk to his slaves you'd get free slaves out of it! Fat stacks of cash right into your pocket!
Serfdom, on the other hand, was also a pretty symbiotic relationship rather than the cruelty we're shown in movies. For every 1 person in a community who provides a service that is -not- related to growing food you need around 50 workers in the fields. Town has a Blacksmith? 50 people producing food. Town also has a priest? That's 100. Tavernkeep at the Pub? 150. Not because 50 workers need to supply that one guy with all the food he needs through the entire year, but because every farmer produced only slightly more than they needed, themselves, early on. Later inventions made it easier to get lots of food more rapidly... but.
So to have a single Soldier or Guard you needed 50 people working in the fields. To field 20-30 soldiers, enough to protect the populace from Banditry or Wild Beasts. Enough to go to war on behalf of the community, etc... You needed a -lot- of people in the fields... Not that them being in the fields meant they were overworked, either.
Food Production, back then, averaged out to about 20 hours a week of work. That's not a joke. You'd go out to your fields at around 7am when the sun was up, feed your animals, go over your fields, tend the farm, until about noon. And that was your work day. You'd then hit the tavern, pub, central square, head home to your family, sing songs, and generally chill out. And that's not including all the Festivals and Holy Days you'd take off which were WAY more common.
Oh, sure, during Harvest time it was all hands on deck 80 hours of work in a week barely time to get a meal in. Rushing to try and harvest all the food before it past it's peak and started spoiling. And then there was prepping it for storage or use as food immediately (Threshing Grain, for example, or grinding flour). But then you hit the Harvest Festival and everyone goofed off getting drunk and enjoying the Entertainment your local Lord hired to come perform.
'Cause the Lord's job wasn't -just- to protect the people, or manage the village, it was also to be the central party planner for a thousand or more people who need a -break- every now and then. And the Lord would get a break every now and then when he was Invited to Court. He and his family basically got an all-expenses-paid trip to the Capital to hang around in fancy places eating nice food and drinking great booze for a month or more, depending on what the King wanted for them.
EVEN THE TAVERNKEEPER only worked around 20 hours a week. 'Cause he'd open at noon and close at night. Before then everyone was in the fields, and with no street lights people shuffled home, drunk, as the sun was setting or shortly after dark, letting their feet walk the same path they've walked for years under starlight. Blacksmith? Did his work in the -morning- before it got too hot to be in a freaking FORGE. You'd tell him what you need on your way to the fields, pop back at noon or early the next morning to get what you need unless he had it on hand. When a smith wasn't forging particular tools for people (Plows, Bands for the Cooper, Axes) he was making things like Nails that you constantly need more of. You might only need 1-2 hammers in your life, but -nails-?!
And kids? Yeah. They worked on the farms or in the house with their parents or cleaned tables in a bar if their parents owned a tavern... But they also got the same holidays and festivals and 20 hour work weeks as their parents. And even during Harvest Time they were largely spared the more brutal quantities of work where they might "Get in the Way". You wanna know why we teach kids in the fall? Yeah. It's to keep them out of their farmer parents' hair during harvest. And it's been that way since forever. Though back then they were more likely to be taught by the local Priest than in an actual school.
And Apprenticed kids working with the blacksmith or cooper or fisherman? Same sort of situation. 20ish hours a week and most of it fairly light labor for the first half of their apprenticeship as they learn from the ages of 8 to 12 or 6-10 (depending on culture) and then more full on labor after that, but still capping out around 20 hours a week because the blacksmith isn't going to stay open during the hottest part of the day just so his apprentice can get in a few more hours of practice swinging a hammer.
The Evils of Child Labor and Ridiculous Work Hours weren't a real thing until the Industrial Revolution. Because unlike a Farmer or a Blacksmith who needed a bunch of time off work with his family and general happiness a machine -could- run 24 hours a day and the owners of those factories wanted them constantly churning out product for the maximum benefit to their cost.
Once society largely shifted over to an industrial one, the idea of a 40 hour workweek went from "Brutal but sometimes needed to be done" to "The bare minimum" in the eyes of society. It is not how humans have existed for the -vast- majority of time we've lived.
We exaggerate how terrible the past was in order to make our present seem more palatable. That's not to say that violence wasn't more common in those times. It -absolutely- was. Or that the world didn't have cruelty in it. It -absolutely- did. But that cruelty was just as shocking and drastic in those eras as it is, today.
And people's day to day lives? WAY less cruel, even for slaves before the transatlantic kicked up, than we imagine today.