It's punishing them because by labeling them "sex offender" for the rest of their lives and letting everyone know that, they're not going to be able to get any sort of decent job, are very restricted on where they can live, and there's the risk of the rest of the neighborhood driving that person out. With little chance to live a normal life, perhaps that's part of why they reoffend
Have anything backing up that 90% figure?
Well, we have to separate the kinds of sex offenders. A rapist, for example, has a different reoffense rate than a pedophile. It's much lower, probably like 3-10% from what I have read. And some statutory rapists, say a 21 year old with a 16 year old girlfriend, are probably 99% not going to reoffend.
A predatory pedophile is a different matter. That's why there are different "classes" of sex offenders. An offender classed at a high level is expected to reoffend in many cases. It's just a matter of time.
Spooky was talking about people who hurt children. And yes, they should bear a temporal punishment for this the rest of their life. If nothing else, it will reduce or eliminate time in purgatory. Children are affected much differently by sex than adults, and always in a negative way.
I don't see what having a difficult life post-conviction has to do with sex crimes. Saying that because they have a tough life is a reason (even a partial one) for them to rape someone else is non sequitur at best.
Don't want to be on the database? Keep your hands to yourself. It's that simple.