This is stupid. The real truth is that something like 95% of all sex offenders are on that list for really stupid reasons that most people wouldn't even consider a big deal at all. It's very seldom that these people actually raped someone for example.
For example, if you go to a web site and the site has some girl that's 17 nude on it you would be be in felony possession of child pornography regardless of if you knew or not. If your computer was searched for any reason at all you'd be going to jail my friends. There was just a story about some celeb photos being released and she was only 17 at the time of the nude photos... you go searching and find the photo, you are now considered a sex offender.
I'm serious. The laws are that crazy. As soon as you get even a little bit involved with the judicial/prosecution people they get your number and you're doomed, you get on watch lists and bam - next thing you know you're a sex offender for practically no good reason.
And this can be applied to any number of things, not just internet porn. A just turned 18yr old having sex with his 17yr old girlfriend...BAM, sex offender. You spank your daughter on the butt and she gets really pissed off and goes to the police to file a complaint - BAM sex offender.
Don't judge these "offenders" so harshly, chances are VERY good you've committed equal so-called crimes as them in your life. The laws are twisted and have swung too far in the name of justice...there are millions of sex offenders now since society got so politically correct and lost all common sense in the last 5 years or so.