Slavery in the U.S. was a huge economic force, one that a certain contingent (the very wealthy) never got over losing. The next best thing was to create whole groups of people who are desperate enough to work for almost nothing. That’s what we have in this country now. And it works best if those people are constantly putting out more children. That keeps them even more stuck and more desperate, and it keeps a steady supply of cheap labor coming.
In my experience the only difference between a certain kind of right-wing “libertarian” person and a slavery apologist is just the amount of time you’ve spent arguing with them. Their arguments (pro-child marriage, anti-abortion, anti-minimum wage) end up converging at “well, in some cases it’s /more/ expensive to provide people room and board than it would be to pay them in cash”.