Hard one this for me, I've worked with prisoners in the past. Some have been genuinely remorseful (one refused early release because he said he should serve his time), others have delighted in their crimes. Now, it has to be said that these weren't sex offenders (the ones I worked with were lifers), but I have to wonder if the attitude was the same amongst all criminals.
Take the Moors Murderers: Here we have two people who, had they been convicted a few months earlier, would have done the hemp fandango. As it is, both were sentenced to life imprisonment. And both have continued to play mind games with both the public and the families of their victims, Myra Hindely was notorious for this and would play on the naivete of people like Lord Longford (who supported her release) and who she could dance rings around claim that she was reformed and it was the nasty Government keeping her locked up, why weren't Amnesty coming to support her.... And Longford believed all her claptrap. He was even siding with her when she said that she would give up the location of the last two graves if she was given early release. Which doesn't sound that reformed to me. Her boyfriend, Brady, has been on Hunger Strike for about ten years, claiming he wants to have the right to die, thus making sure he gets the limelight of publicity shone upon him. Both he and Hindley were acutely aware how much distress it caused the families of their victims each time they did something to end up in the papers. As I said at the beginning, a few months earlier and they would both have hung and I can't say the world would have missed them.
But, of course, what if someone does reform? What if, when they get out, they want to make amends for their crimes? If we execute them, then this chance is taken away from them.
I can't answer it, I'd say that putting someone on a sex offenders register for life should help, but that each person put on it should have their convictions looked at to see if it actually warrants it, which to me at least, pissing in a back alley doesn't!