STDs are mainly found among the poor, because malnutrition weakens the immune system. Poor people in the USA are less likely to be circumcised, poor people in the EU are more likely to be circumcised (Hispanic v.s. Muslim immigrants). So STD statistics can be misleading.
Common sense tells us that both reduction of STDs and loss of sensation are likely if thin, moist, but highly enervated skin is removed. So both sides tweak science if they deny either.
Note: Many adherents of Dual Seedline Christian Identity also believe in ritual circumcision.