Earlier quoted context omitted.
What a paper! And you missed an even MORE relevant excerpt!! Man and Slave The problem, and it is a moral prob- lem, with which we are here faced is very close to one of the great problems of slavery. Let us grant that slavery is bad because it is cruel. It is, how- ever, self-contradictory, and for a reason which is quite different. We wish a slave to be intelligent, to be able to assist us in the carrying out of ou…
> Complete subservience and complete intelligence do not go together. Isn't this contradicted by the centuries of slavery in our history? Or is the author arguing that the people who were enslaved did not have human-level intelligence (which would be rather a problematic claim)?
This isn't contradicted by millennia (not centuries) of slavery because it was forced on the enslaved populations against their will.
> Or is the author arguing that the people who were enslaved did not have human-level intelligence
He gives an example of "a clever Greek philosopher slave of a less intelligent Roman slaveholder." Does it sound like he's arguing that Greeks were not of "human-level intelligence"? No.