I've also read that issues such as poor nutrition during pregnancy can have heritable effects lasting for several generations (so by this model, even if all the impoverished people in the world were suddenly given all the best resources, one wouldn't expect to see significant intelligence/behavior improvements until their great-great-grandchildren or so).

For a bayesian who thinks about whether to hire a black person or a white one, it's irrelevant whether intelligence difference are due to parents being poor and haven't eaten enough food during pregnance or whether they are due to genetic differences.

As far as I understand the social justice movement they would approve of both justifications because both are essentially that the person gets judged by their background and get's treated as a member of an underclass.

I can't remember someone on lesswrong making a claim as strong as claiming that black should be stopped from procreating by eugenic measures. You find people who argue that overpopulation and African getting children is the central problem of humanity at the moment but nobody is making the argument directly.