I suspect that Khan’s reflexive criticism comes from a place of exasperation with the idea, still in circulation among some social scientists, that race is “just” a social construct or that the racial categories used in the US today are entirely meaningless.When social scientists say racial categories are "meaningless" I doubt many of them think that perception of race - and racism itself are "meaningless." They are certainly aware that there is a group of people in the United States who have been treated with horrific injustice, and that horrific injustice is based on the group's ethnicity, and that ethnicity has been characterized as "race."
An analogy would be theism - many social scientists are atheists themselves, but certainly don't characterize theism itself as "meaningless."
As usual, a cultural materialist approach is helpful. Anthropologist Marvin Harris used terms to indicate different perceptions of a culture based on whether one was trained as a scientist (etics) versus a participant in the culture itself (emics.)
In 1993 in the journal "Social Forces" Harris and three other authors addressed the issue of the fluidity of racial classifications in an article called Who are the Whites?: Imposed Census Categories and the Racial Demography of Brazil.
I think science writers want to give Khan the benefit of the doubt - after all, the guy is one of them, a science writer himself, and he's been given respect from mainstream outlets like Discover: surely, they figure, his belief in race cannot be as extreme as it seems. So they struggle to find common ground with him.
However, for all they claim they are not opposed to race as something besides a social construct, the Vox article describes the ever-changing nature of this social construct. The changing perception of Europeans is an excellent example:
Finally, we ignore some ancestral differences and focus on others when we categorize people into races. As a historical example, consider Carl Brigham’s 1923 book, A Study of American Intelligence. In a section titled “The Race Hypothesis,” Brigham attempts to classify people from different European countries in terms of their “Nordic,” “Alpine,” and “Mediterranean” blood: The Italians are estimated to be 70 percent Mediterranean; the English as 80 percent Nordic.
The effort to divide Europe’s inhabitants by “blood” is crude, but in one respect, Brigham wasn’t wrong — with modern technology, you could certainly differentiate a person with English ancestry from a person with Italian ancestry. But sometime in the past century, we stopped conceptualizing the differences between the English and the Italians in terms of race. We elevate to the status of “race” the distinctions that are our current political and cultural preoccupations, while eliding others.
Yes, you can classify people into ethnicities. But race is a whole different story. A contemporary example is Latinos, who are generally considered "people of color." However, some Latinos consider themselves white. Who is to say whether they are right or wrong? Nobody, because clearly the label is completely subjective.
Ultimately what it all boils down to is that Khan, Murray and other proponents of "race" really just want to believe in race, and want to believe that contemporary African American problems, so obviously begun in slavery and continued for another 150 years of varying levels of oppression, are no longer due to injustice but rather due to biological inferiority.
But when you analyze their claims they fall apart. Which doesn't bother them at all. They just call anybody who questions their claims anti-science and politically correct.
When theists say atheists must prove there is no god, atheists respond that they are not obliged to disprove somebody else's claims, the obligation falls on the claimants to prove their claim.
This is why it's up to those who believe that race is scientifically valid to prove it. And so far they have failed miserably.
And like many theists when speaking of atheists who demand proof, Khan claims that race skeptics are "close-minded."