Why sex crimes and not violence? There is data that shows when you are older, you stop committing violent crimes (not nearly as many 50 year old muggers out there as there are 20 year old). This is why 3 strikes laws work - you take the 20 year old and lock him up for 25 years and when he gets out he is past his young testosterone phase.
As for sex crimes, the recidivism rate is damned high. Child Molesters have a rate of >50% within 5 years, for example.
The Department of Justice has a report on this (which quotes academic research):
http://www.csom.org/pubs/recidsexof.html
Now, does this justify the various scarlet letter laws? Tough Question. As a parent, if there is a 52% chance that a child molester will strike again, I want to know if the neighbor is one. Then again, as we apply these laws retroactively (the registries being seen not as punishment but as information), people who pled guilty long ago are regretting not going to trial.
There are other side effects of these laws. Some states ban a sex offender from living near a park or school - sounds great, right? Except that the offender is now effectively banned from living in ANY urban or suburban area. A map of California was run in the local papers showing that a sex offender would not be able to live ANYWHERE except the desert or the farms if they were banned from living near parks or schools. Rural police are not too happy about this either.
http://www.usatoday.com/news/nation/2007-02-25-sex-offender-laws-cover_x.htm
So I will admit to being torn. ASSuming a fair trial and a true sex offender (let’s use the extreme of the 50 year old man and a 4 year old boy just to make it purely nasty), I would prefer death. After that, life in prison. After that, castration (if that actually worked). After that, registered sex offender list. Simply, I want the best possible guarantee that the perp will NEVER again molest a little boy.
But our court system sucks. It is biased against people who can not afford a decent attorney. Sex offenders start off on a bad foot just by being accused. I don’t know if a fair, impartial jury is even possible.
In addition, the laws have been written so that (per an earlier post), giving condoms to a 13 year old is an offense. Urinating in public can qualify you for the list if a kid saw you. High school boys who turn 18 in high school suddenly are offenders if they are sleeping with their 17 year old girlfriend (again, it depends on the state and jurisdiction).
We are willing to let 9 go guilty rather than the 10th go free - a policy I agree with. It is just very hard to reconcile that (personally) with letting child molesters out on the streets without knowing who and where they are.