Only if you ignore the ability of the human body to adapt and evolve.
Large swathes of the United States would otherwise be de-populated of Caucasians through skin cancer and other environment-induced malignancies.
Still, there are sufficnet numbers of Caucasians that produce sufficient levels of melanin to survive in most of the United States South of Louisville Kentucky ~ particularly if they have air conditioning.
At the same time, you take away science and medicine they'll just be sweaty old cancer patients