Fair enough, but we are so close to the point where we could actually fix these group differences by applying positive eugenics. Couple goes to get gene therapy, the kid comes out smarter for it (and we could also erase certain genetic diseases while we're at it). Everyone would be better off. But we can't do any of this unless we acknowledge the reality.
As for why some would avoid this field, the answer is rather obvious. The people who step out of line are subjected to intense harassment.
Yes, I realize that Nijenhuis' numbers are not perfect (there are some other criticism one could make besides the ones you pointed out). But again, that's all we have. As for the language argument and the likes, this is why I prefer to use US numbers to establish the gap. They are much better established findings, with much larger sample sizes and without any language bias.
As for any possible cultural bias, we can have that debate if you want. But for now, I would leave you with this. Experts don't think that they are biased. We can go into detail on this topic if you want.
The only 'fixing' which is not science fiction/dangerous is that people can detect if the child will be born with some serious ailment, eg down syndrome, and opt to terminate the pregnancy while it is legal (timeframe). If you actually think that current medicine can increase the child's iq, and moreover has no side effect/is accurate, then indeed you live in a fantasy, which may be dangerous itself, Hehehe. First do no frigging harm.