Except that slaves also make new slaves that can be sold.

I really dislike this idea that slavery was just a cultural aberration and not economic. For one thing, that lightens the moral stain of slavery adjacent activity, most notably colonialism and the exploitation of the colonies. This never went away. Economic colonialism exists to this day. We just call it “outsourcing”, “offshoring” and “subcontracting”.

Offshoring generally improves the lives of the people who get the offshored jobs. Usually foreign companies pay more and have better working conditions than the local companies.

It's worse than that because it takes something that should beg the question what modern things we peddle today because they make $$ are in fact morally wrong into a trite "hurr durr past people bad we smart now" that nobody learns anything from.