Human biodiversity ought to be an unremarkable idea, as self-evident as the laws of identity or of cause and effect. It should be especially obvious to the secular mind which believes the human race is wholly the product of unguided evolution. If the beasts gradually adapt to their surroundings then it's not a great stretch to suppose that humans adapt similarly. However, HBD is treated as a dangerous idea that leads to fascism, at best. Its critics point and sputter about how only a terrible raciss could believe all of that stuff Steve Sailer writes.
To the Christian mind, HBD is theologically irrelevant as every human being is created in the image and likeness of God and everyone is called to do good and avoid evil. God does not judge us on whether our IQ is one standard deviation above or below the median. But it shouldn't be difficult to see how a widespread acceptance of HBD would radically alter our public policies. This is why race consciousness must be ruthlessly suppressed because otherwise the American people would elect the cryogenically frozen brain of Hitler as president... or something.
Our natural tendency toward race consciousness explains why we tend to self-segregate. We naturally gravitate toward those who are more like ourselves. It's not a coincidence that accepting diversity as a public principle has resulted in an ever larger and more intrusive State to prevent people from Noticing Things. Modern egalitarianism is less geared toward restraining violence toward the other and more toward making whitey pay.
In a technocratic liberal society, a person's worth is largely determined by going to the right schools, earning the right degrees, taking the right jobs, and hanging out with the right people. Liberalism purports to level the playing field and grant everyone equality of opportunity. We are no longer bound by strict social, political, or racial hierarchies. However, these things are unavoidable in practice. The social hierarchy becomes arbitrary and incoherent as opposed to disappearing all together. A man with an IQ of 85 probably will not reach the same heights of material advancement as the man with an IQ of 125. To the liberal, this is to assert that the former is inferior to the latter. It is to assert that the latter has license to oppress the former, which is why we need a powerful State and strong public pressure to suppress this line of doubleplus ungood crimethink.
To the modern mind, this appears to be an unsolvable riddle. HBD is probably true, but it's an ugly truth that will lead to violence so we have to spread the noble lie of Zero Group Differences.
I'll give you a hint: there is no riddle if you're not an ateleological reductionist.