There have been societies in the past that castrated young boys for a variety of reasons. Italy did it at one point so that the boys could become opera singers, and ancient Arabia did it so that rich men could have eunuchs to watch over their harem girls without fear of the eunuchs sleeping with them.
I think this is even more damaging than female circumcision, because when you castrate someone, you not only stop him from ever enjoying sex, you also stop him from ever being able to have children. And while a society might find female circumcision customary, and therefore a woman will at least be able to marry and have a family even if she's circumcised, there's a good chance that no one will want to marry a castrated man, since he can't have kids or have sex.
Yet men never flip out over this the way women flip out when you mention female circumcision. It's like they can't be reasoned with when you try to discuss it with them. They immediately jump to talking about how barbaric it is, how it should be stopped, and so on. It's like you can't even sit down and have a rational conversation with a woman about this.
So why are women so much more sensitive about female circumcision than men are about castration?
Answer on Men don't flip out over societies that castrate boys, so why do women flip over female circumcision?
Women simply lack any empathy towards anything other than one of their own. They are truly sexist and bigoted.
They simply are gender narcissists who believe men are inferior in many ways (intellectually, aesthetically, morally, etc):
"Women are nearly five times more likely to show an automatic preference for their own gender than men are to show such favoritism for their own gender"
"A clear pattern shown in all four studies is that men do not like themselves automatically as much as women like themselves,"