I think any strong counterfactual belief makes one stupid roughly in proportion to how counterfactual it is.

For instance, young earth creationism (YEC) leads people to routinely deny basic results in physics, chemistry, biology, geology, astronomy, and anthropology. At a minimum.

Garden-variety racists might have their stupid side, but I think YEC's have them out-stupided.

Racism requires some degree of moral degeneracy that YEC does not, but it doesn't require as extensive rejection of and incomprehension of relatively straightforward observations.