And of course it still is - slavery is legal as a form of punishment in this country and we have prisoners working at pay and conditions below those of other forms of wage labor. Is it your hypothesis that the two don’t interact with each other? How could they not in a market context where forced labor persists in competition with other low wage labor?
It's only a fundamental reality of the human condition if you're not born into wealth. So, not really fundamental at all. A fundamental component of slavery is there being a master. You're sort of ignoring that wage-slaves are in fact, creating wealth for someone else.
The "exception of born into wealth" sounds a lot like the ancient Greek nonsense of philsophers and aristocrats justifying slavery ironically. While they themselves were willfully ignorant of actual means of wealth generation and thought it had to be stolen by conquest and holding traders in contempt.
And this sickness was modeled into the Antebellum US South combined with the projection of accusing the North of wanting to enslave everyone.