as I hear it, the Sex Offender's Register doesn't actually list what the charges were. So people who have been charged with minor offenses like public nudity, urinating in public, or soliciting a prostitute would have been banned along with people who've committed more serious crimes.
A report by Sarah Tofte of Human Rights Watch, a pressure group, found that at least five states required men to register if they were caught visiting prostitutes. At least 13 required it for urinating in public (in two of which, only if a child was present). No fewer than 29 states required registration for teenagers who had consensual sex with another teenager. And 32 states registered flashers and streakers.
I detest the idea of penalizing someone for a crime permanently. If they were on parole, sure, but once you've served your time you should have the same opportunities and rights as everyone else. Not doing this creates a oppressed subclass in society that is already predisposed to criminal behavior - guess what that does for recidivism rates?