I think he means that that argument sounds similar to the ones actually given by slavery's supporters. I've heard an old economic argument that chattel slavery is better than wage slavery (what we have now), because you treat something you own better than what you merely rent.

(So an anarchonistic example is that a car you own will remain in better shape than one you rent. That's actually not such a terrible argument, though of course we'd reject it nowadays.)

That said, I don't personally know either way, and Wikipedia does mention that _Uncle Tom's Cabin_ is popularly seen as propaganda. (I personally haven't read the book, but it wouldn't surprise me if it were 'propaganda' in the sense that it was biased and promoted a political point of view. Apparently, before the Nazis, propaganda didn't have such bad connotations.) http://en.wikipedia.org/wiki/Uncle_Tom%27s_Cabin#Literary_si...