People unwilling to entertain the possibility that genetics differ between ethnic subgroups are indeed failing at rationality
Those people are failing at something much more basic than rationality. Likewise for folks who think intelligence does not have any basis in genetics (try to debate a douglas fir!)
It is obviously true that different people differ genetically, and obviously true that intelligence is related to genetics. But it is not obvious in this way that differences in intelligence between two humans would have anything to do with genetics.
Those people are failing at something much more basic than rationality. Likewise for folks who think intelligence does not have any basis in genetics (try to debate a douglas fir!)
It is obviously true that different people differ genetically, and obviously true that intelligence is related to genetics. But it is not obvious in this way that differences in intelligence between two humans would have anything to do with genetics.