This McCuen guy's comments on slavery, as presented in the article, are dumb. He posits America's choice during slavery times as between having slaves and having free Africans as countrymen. McCuen ignores the option of never bringing slaves to America to begin with.
That said, the article also discredits McCuen for observing that blacks don't do as well on standardized intelligence tests as whites. This is a consistently-observed phenomenon with widespread social implications. Right now in California we have a judge throwing out the state high school exit-exam requirement because fewer blacks passed the test. Previously the University of California lessened its reliance on SAT scores solely because blacks post lower SAT scores.
The left opposes all testing because the left wants a society devoted to group entitlements rather than individual accomplishment. The left claims that all tests are racist. We shouldn't let them get away with eliminating testing and the concept of objective merit.