I found the following on a site devoted to the femdom chastity fetish. Can’t find it again now or I’d post the link.
A distinct but not uncommon fantasy is emasculation and castration. In a pretend/role-play scene, there is nothing wrong at all with this. In fact, chastity, particularly long-term chastity, indefinite chastity or permanent chastity, play well with this fantasy.
Putting a man in chastity involves taking the freedom and use of his penis away from him. He can’t have sexual pleasure. He can’t touch himself. He can’t masturbate. His daily functions are affected. He has to sit down to urinate, unlike a fully functioning man. He cannot scratch himself, as a fully functioning male can (and often does). A man in chastity is no longer a fully functioning man. A wife who locks her husband in chastity effectively castrates her man.
No word has a greater effect on the male psyche as “castration”. The word ignites fear, insecurity and phenomenal nervousness for a man. It threatens his identity as a male like no other. A woman who jokingly refers to castrating her husband sends a scary and challenging message to her man. The wife who locks her husband in chastity and tells him that she is castrating him, asserts that his whole identity as a male is in her hands. For her husband, it reinforces his submission to his wife, his chastity being indefinite … maybe even permanent. His future may be as merely a doting eunuch in service to his beautiful Empress, serving to cater to her pleasures and desires.
I must admit, this fantasy turns me on incredibly. It reinforces my control in the act of locking the device on my husband. The click of that padlock becomes the sound of emasculation – the castrating snip. Sometimes I will say to my husband when I am about to lock him into his chastity device “Darling, it’s time for your castration!” or “tomorrow I will be castrating you”. His timid and resigned response to such a simple sentence of six words excites me incredibly. And I reinforce it continually after locking, referring to his castrated state, or reminding him or myself out loud in his earshot that it has been only so many days since I castrated him. Essentially it tells him that his predicament is indefinite, and subject to my decision, and there is no point in discussing release.