Tell me you don't understand the complexity of the psychology behind why people rape, or the variety of causes of unacceptable sexual attractions.
If someone is paedophile because at some point as they grew up, the age of the person they're attracted to did NOT grow up with them.. say they hit 12, are interested in 12 year olds - but as they get to 15, 16... they're still* interested in 12 year olds...
Then choosing medication that stops sexual urges, or indeed, castration, is likely to have some degree of success.
However that is a tiny minority of sexual offenders (and those taking that option have very often not committed any sexual offence at all, they know it's wrong and don't want to, hence making that choice).
Rape is about control, its about force, it's about getting what you want, causing fear and panic in someone else. It's about putting your needs above anyone elses.
Sexual abuse of children can be the same - a person is making themselves feel good, by making someone else feel fear, terror, pain, helplessness, humiliation.
The ability to get a sexual thrill out of that is not generally relevant - it still feels good to them, its still exciting, their brains still become aroused and are fulfilled by the things they do.
So cutting off their balls (Which certainly doesn't actually remove all sexual ability or arousal anyway - I live with two castrated male dogs who can both get an erection, hump, be sexually aroused... and dog physiology is not significantly different to human!) won't help.
It would provide a false sense of security for many people though - it would actually be dangerous.
*I know that the word actually applies to a younger age group but it is the one most people use.