Why do you think there is so much opposition towards it?
Because it's invariably agenda and value driven, stacked to favour certain biases, and funded by xenophobes/sexists who want the results to use as propaganda.
A more productive and fair-minded approach to studying disparity in intelligence would be to study and account for actual relevant factors such as poverty level, access to education, nutrition, etc, instead of ethnicity, nationality, skin colour, hair colour, genitals, shoe size, etc.