Classic economics. It focuses on the one idea without any thought of what might break the model. These kinds of hypotheticals are only for learning the basics so you can move on to bigger models. I'd say you're at maybe freshman econ level - which is good, since you're trying.
Now, tell me one place on earth where slavery has never existed. Idk, maybe it exists. How about one place with no rent seeking behavior? No dominating special class of people?
Dude, even after we had this global second enlightenment and banned slavery, it only took us a couple of decades after finally ending its disguised form (Jim Crow) to reinstitute slavery on mass scale in the form of monetary debasement.
So your model is incomplete. There's something perpetually incentivizing a suboptimal, nonvoluntary form of organization. I have ideas, but I want **_you_** to have ideas. Seriously think about this.