There seems to be very little data on castration but I found this:
In Denmark in the late 1950s and early 1960s sex offenders were permitted to choose prison or surgical castration. Research on 900 castrated sex offenders showed that the rate of repeat offenses was low, about 5 percent. But 46 percent of the men said they continued to have intercourse.
We know child rapists aren't going to be locked up forever so personally if they're going to be let out anyway I'd rather they'd been surgically castrated.
PP's say castration doesn't work because you can still have sex but rape isn't about an uncontrollable sex drive, it's about power and violence - but when your testosterone levels are far lower, even if you can still have sex, I'd assume the angry, power hungry, dominating side of you is going to be reduced right along with your sex drive.