You people really have huge gaps in your knowledge.
Castration will not stop a man ejaculating. The bulk of the ejaculate is produced in the seminal vesicle and the prostate gland. The sperm is produced in the testes but is just a tiny part of the wallpaper paste.
As far as preventing a paedophile getting an errection goes, then history has shown that they will simply use a broom pole or whatever which will be even more damaging. Only incarceration will prevent paedophilia (or euthanasia).
joe