The only reason I say this is because unlike many other types of criminals, these monsters are well known for being unable to be rehabilitated. They notoriously re-offend over and over and over again. The statistics for their improvement are miniscule. It's way too high a risk to turn them loose in society. The offense is way too heinous to risk it. The results to the victims are astronomical in proportion to some other kinds of crimes...not murder, but some non-dangerous or not directly dangerous crimes.
What should happen to sex offenders after they get out of prison? Should they be exiled to a "sex offender island"? Should they be locked in some sort of compound?
It's easier to re-offend if you're labeled as an offender. You move into a house and EVERYONE knows you're a sex offender. You apply for a job, and your employer knows. Why even try to change? You already have that label- it doesn't matter if you stay "clean" for the rest of your life or re-offend.