We can reject the existence of an observed natural phenomenon because we can't explain it. We still haven't unified gravity with the standard model, but that doesn't mean we reject that gravity exists (for practical purposes or otherwise).
The fact that a natural phenomenon might be socially inconvenient is even less of a good reason to reject its validity.
Finally, I don't even see why it should even be so socially inconvenient. Say the experiments are right, and intelligence is mostly heritable rather than a result of education, upbringing, etc. Why should that justify entitlement on the part of the wealthy? Indeed, it should cut across that grain. If its mostly heritable, being intelligent shouldn't be seen as intrinsically virtuous any more than is being tall. Moreover, the heritability of intelligence may very well imply a need for a change in our priorities when it comes to social welfare. E.g. maybe we need to de-emphasize education, and divert resources to building up social and family networks.
"Socially inconvenient" doesn't even come into it, because twin studies don't tell us anything about differences between two ethnicities. For that matter, genetic diversity within populations might have a larger effect...
The "intelligence is genetic" "fact" is often used to justify refusal to tackle socio-economic problems (like "under-achievement" in blacks or hispanics in the US, or the turkish minority in my home country) with socio-economic solutions. Because hey, it's all genetics, so we can't change it. Even if measures for improvement have been proven...
The fact that intelligence is heritable says nothing about social-economic policy for changing the environment. It is as absurd as saying that because "height is genetic" there is no reason to worry about malnutrition.
Changing it wouldn't make a difference, everyone using that logic isn't basing their end goal on it, simply using it to justify their feelings.
Hell it took a while for me to understand the benefit of such improvements, and it had nothing to do with genetics. My problem was few people talk about the socio-economic impacts on capabilities, and the fact that counteracting programs can theoretically stop the death spiral in those groups.
However there are a lot of people who can't get over "not like me" and think the whole thing is a waste because it takes away from "hard working young men".
The fact that a 'wrongness gene' hasn't been, and may not ever be, identified does not undermine my assessment, but rather indicates current models of the interaction of genes and wrongness might be naive, and the interactions are probably deeper and more complex.
To take an extreme example where genetics is the clear cause, cats are underrepresented in college. Because we know that cats are genetically less intelligent than humans, we can conclude that affirmative action/college for cats education programs/etc are a waste of money.
Another use would be knowing that if only 50% of the population has the intrinsic intelligence for college, college prep programs should not serve more than 50% of the population (modulo technical details).
Not saying it's moral, but definitely and obviously practical.
Pedigrees and genetic testing in animal breeding are way more useful. But there you have completely different structures and goals. And some of them, particularly diseases with high heritability like canine hip displasia, can't be solved by current genetics yet.
As long as you can't tie intelligence to particular genes, as long as you can't tell what amount of intelligence in an individual is inherited, and how much isn't, there is no use for this in education, politics or social welfare.
What I see the argument being used for, mostly, is to justify racism and entitlement issues in wealthy people...