You’ve already got for-profit prisons in the US where inmates (slaves) are hired out.

What do we know about how a for-profit system works? That’s right - profit must always keep growing, or to put it another way, incentivising the process of creating criminals in order to increase the potential for a growing slave labour market is a growth industry.

Just because something doesn’t have the literal name ‘slavery’ attached to it, doesn’t mean it isn’t actually slavery in every respect that matters.