You know, I've never heard about an opera related to the topic: 'Il Castrati'. It commonly refers to castration, but there is a long mystery around theme. No clues about this torture have been undercovered despite Rossini was one of the first Castrato in his youth. Weird, right? A very well known musician, a genius, and the mistery hasn't been discovered.
On the other hand, it's said that there was a generation of Castrato (hardly to find in society with such skills) with some other sexual inclination. I just imagine: a conservative regime would never allow any homosexual sing before the Pope, Cardinals; even politicians were forbidden from their wonderful music.
I think only the upcoming Reinassance produced Il Castrati went somehow public. The pressure of the church over blooming muses for the artists, a relief for the souls of the selfless misses and hopeful ladies simply can lead to censorship the font of happiness.
A legend: this lady, already married, lost between the chances having none for her after the promess the world was meant to change at a spark of sacrifice, passes away through the right tone, the right lyric, the special voice. What happens if next time she dies because of self-love? It is dangerous for the whole Kindom to hears the Castrati choir again! It makes everyone happy also! They are just kids playing elegant dandies meanwhile they become men!
Il Castrati dessapeared 2 centuries later, replaced by a heroic Tenor to delight the opulent. Never were part of a real Opera, except as subsidiaries. Maybe their idea, like the perfect scape of the perfect Reinassance.