I completely agree with them and with you. But there are two side big "however"s attached.
First: bris. Every negative thing you can say about FGM has been said about bris. Do a search-and-replace on key terms and all the arguments have already been made.
Second, I'm sure supporters of this practice would say, "Some people are going to do this anyway. Isn't it better to have it done safely by a medical professional?" And isn't that one of the arguments supporters of legal abortion have been using for decades? Why is it a valid argument in one case but not the other.