Kevin – I’ll take a crack at the mystery. Perhaps I’m wrong, but it seems to me that this is a pretty common argument on the left. For obvious and good reasons, slavery looms very large in the pantheon of evil for the Left. Again, that is at it should be – for everybody. But for a very, very, long time the left has been eager to make slavery — an institution that stretches back to prehistory on every continent humanity has existed — into a particular and unique sin of capitalism. This guilt by association goes back at least to Marx:

Without slavery you have no cotton; without cotton you have no modern industry. It is slavery that has given the colonies their value; it is the colonies that have created world trade, and it is world trade that is the pre-condition of large-scale industry. Thus slavery is an economic category of the greatest importance.

Marx was wrong, of course. That’s not say that slavery wasn’t economically important, particularly to the South. But it’s not really true that slavery plays the central economic role critics of capitalism have long claimed. But it does feel true to a lot of people who want America and capitalism to be the poisoned fruit of the tree of racism and slavery (the claim also feeds into arguments about things like reparations — America got rich off of slaves and therefore they should be compensated).

I don’t know jack about the author of that anti-Rand piece, but it reads like the kind of thing written by someone who swims in the sorts of waters where such assertions are taken as fact. “We all know that capitalism and America are the Romulus and Remus of racism….blah blah blah.” With such confirmation bias in place he probably googled around for some damning stats and didn’t even bother to check the math because they simply had to be true.