This isn't the first time this has come up. In 1995 Larry Don McQuay wanted the state to castrate him. He even threatened that he'd repeat his crimes if he did not. I remember it was in the news quite a bit. The state eventually released him saying he'd have to pay for his castration. According to
this article he was back in prison in 1997. In his case I remember it was reported they were unable to find someone willing to perform this procedure on him. Since then, according to that article, Texas has passed a law making castration available to child molestors. I wonder if anyone has taken this opportunity up.
At the time there was much debate about this with many weighing in as some of the above posters: castration is not necessarily going to stop this people from repeating their crimes. I agree with them. Is there more at work than hormones here? There certianly must be. If someone wants to be castrated fine but I wouldn't look at it as any sort of guarantee.
One of the other articles I found with a quick google search mention chemical castration was considered in California. It would have required weekly doses. Somethings tells me that wouldn't have worked either. I wonder what became of that.
The punishment should be extremely harsh for these offenders. I'm thinking many many many many many years behind bars. About ten times the eight or so Larry Don McQuay was originally sentenced to.