I will try to argue against them from a pragmatic point of view.
The US sure is the top dog in scientific research, but far from the only dog. New competition has arisen, mostly Asian countries that do not care too much about historical Western traumas and sensibilities. The US is no more capable of blocking certain research worldwide that the Pope was, back in the Early Modern Era.
By blocking intelligence research in the US, the US is basically ceding the ground to those competing countries on ideological grounds. As a result, they will get ahead and possibly discover new facts.
(At this point, too many smart readers will wave the suggestion away with a bland "Intelligence is too complicated to be ever really understood." Sorry, I don't believe that. Intelligence is surely complicated, but so was atom splitting. It would be strange if there were never any results in the field, regardless of work spent.)
Which means that a generation or two down the road, strategic adversaries may have tech to alter intelligence and other mental traits, because they will know what to edit and how. Perhaps not that much, but who knows how genetic and epigenetic manipulation in human beings is going to look like in 2070.
Such an ability may prove even more world-changing than the atomic bomb, and the US is shooting itself in the foot by making sure that it won't be able to compete on the field early.