But this is, if I recall correctly, not endemic to the Muslim world, but rather to certain cultures and nations.
Just to be fair.
The originator of this thread may find this practice as horrible as you.
Agreed.
FGM is predominantly an African problem. The majority of FGM is practiced within Muslim societies in Africa, but it is also practiced within Christian societies within Africa. The Shafi'i madhhab is the only branch of any religion that requires FGM.
The country with the highest rate of FGM is Somalia at 98%. Somalia is >99% Muslim. However, Niger is also >99% Muslim, and only 2% of its population has undergone FGM. Indeed of the 0.3% Christian population in Niger, 55% have undergone FGM.
So as you say, although it is not endemic to all Muslims, the majority of practitioners are Muslim, although there is also a significant Christian component too.