Normally you look for deficits in people in order to account for them with special help, but this is a science just looking to shed blame. It's like testing for dyslexia to find kids that you shouldn't bother trying to teach to read. Or even worse, retroactively justifying your decision not to teach redheaded kids how to read by doing a survey of redheaded kids who were never taught to read, over a dozen generations, and finding them stupid.
That's the problem. The field is hopelessly tainted, and being an area that would be difficult under any circumstances (due to mass social effects rather than mass genetic effects), meaningful designs would be hard to find even if the researchers were motivated by something other than justifying the past.
In my experience, the people most obsessed with arguing and proving the usefulness of IQ are somewhere between 110-120. The people obsessed with the heritability of IQ and the supposed dominance of nature over nurture are often people who have raised terrible children.
aside: one thing I'm curious about and haven't found is that there are a number of researchers who show differences between American black achievement (slave descendants) and black immigrants from Africa and the Caribbean (who started arriving in 1965.) I haven't seen a lot of race science speculating about that: did slavers (either Western or the Africans who sold them) have some sort of filter that only put the stupid blacks into slavery? Were all the smart ones culled, and/or their intelligence intentionally bred out of them over generations? Did the admixture of the genetics of so many white slavers into their slave stock lower slave intelligence, or raise their propensity to violence? Or does that entire line of inquiry (or intense study of slave breeding in general) hold no interest for people trying to justify 18th century race science?