You defeat your own argument when you say "there's no culture or anyplace where you'd be glad unless you've been indoctrinated" You're pointing out the very means by which that can and does happen, but I won't dwell on that.
Slavery is evil, but trying to pretend there are no cultures that had it as a cornerstone of their society is foolish. Ever heard of Rome?
Not putting up any resistance to those that are more powerful than you is quite common literally every where. Do you pull over for the police? Are you cordial with police when they pull you over for no reason? Have you ever heard of civil asset forfeiture? These are things that exist in your world. They are not unbelievable or immersion breaking.
I'm not making a moral judgement about how things should be, simply pointing out how things actually are for the majority of people.
Lastly, if you work for a living surely you understand that if you are not productive you will be cut off from a revenue stream yes? You're aware of what happens when someone has no income yes? This is what I meant by be productive or die being a reality for most people. Be productive or die also transcends being a fact of all human civilization to being a fundamental law of nature for all living things in the world.
Sorry I had to amend this to ask, what do you mean when you say? "You can't really claim it's a difference of culture and you can't claim slavery is tied to culture."
The definition of culture is "the customs, arts, social institutions, and achievements of a particular nation, people, or other social group."
See how it says social institutions? Slavery is a social institution.