Oh, believe me, I am in no way saying that nothing should be done about or to rapists and child molesters. I'm a parent too, don't forget, and I've known people whose lives have been devestated by sexual abuse.

I like unusual information, mostly of the historical nature, and had read that the Castrati were often involved in sexual relationships. So, I did a little more sideways digging into the truth of this.

The following statements are taken from:
Google Groups: soc.support.transgendered
in regard to whether or not a castrated male can acheive an erection.

1. Yes, though it's likely to be far less spontainious and short lived. Keep in mind that the testis and their hormones are gone but all the other plumbing is intact and functional. I know this from two people I've known who were castrated by their own choice and found that erections were possible with help from their lover.
2. I guess the answer to your question is that hormones, in this instance testosterone, are only chemical messengers. Even without the messengers, the _structures_ in the body (in this case the erectile tissue in the penile shaft) remain in place and potentially operable. If another "message" can be delivered via the nervous system or via the use of other chemical messengers, those structures are ready and able to function. For more background, you might want to look up the causes of priapism and see if some are strictly related to circulatory functioning, psychosis, etc.
3. You are correct... erection is possible after castration but it is dependant upon the individuals endocrinological profile.

The primary data point here is that androgens are not only produced in the male testes... they are also produced in the adrenal glands for instance - in both XX and XY human genotypes. The level of androgen production varies and may be high enough in some castrated males to initiate erection upon arousal. This adrenal production of androgens can cause some anatomical anomolies in XX people - it is called Congenital Adrenal Hyperplasia and can be a form of intersex in genetic females (it also causes other metabolic problems which are sometimes life threatening). Conversely, the testes produce a fair amount of estrogens... enough to completely feminize a male whose cellular receptivity to androgens is lacking. This is called Androgen Insensitivity Syndrome.
...I think that priapism may be a sort of issue unto itself and, I
believe, more related to the nervous system. It is an interesting thought though... would someone with priapism retain the syndrome after castration? My guess would be yes because I _believe_ the etiology is CNS related. Hormones are my schtick though.

4. Yes, but the definitive anwer is, "Sometimes."

The adrenal glands ALSO produce testosterone, and are, in fact, the main source of said hormone in women. In SOME castrated males, this is sufficient to allow continued sexual function. As I understand it, there was a study done of soldiers who were castrated by a particularly nasty mine the Germans used during World War II.

A short article on the effects of castration:
Go Ask Alice!: Castration effects

A personal story from a gay male about the effects of his personal castration:
Being a Castrated Male

A historical perspective on castration, especially referring to eunuchs:
Eunuch

Ultimately, full castration, removal of not only the testes, but the penis as well, would be the only way of preventing a man from using the organ as a weapon against others. That wouldn't prevent some deranged lunatic from thinking up some other way of harming others in a sexual way, in fact, it might make them even more devious.
Keeping them out of society is the only true way to make sure they won't do anything ever again.