Well, I don't want to stand up for sex offenders, but many studies show that some sex offenders are treatable (but, of course, not all). For example, meta-analysis of sex offenders on cognitive-behavioral treatments showed 19% recidivism rate for treated offenders and 37% for untreated offenders. Even with that difference, this shows that the majority do not re-offend (the follow up period was from 12-16 years from first offense). This was done by Hall and can be found in the Journal of Consulting and Clinical Psychology (1995). There are also hormonal treatments that seem very effective for some (with recidivism rates as low as 1% in some studies). Still, we as a society may not be comfortable with any kind of recidivism rate for these offenders.
Luckily for this case, LE believes this guy had nothing to do with missing Haleigh. Let's hope she's found alive and unharmed soon!
[I should add that SO does not mean child molester in the study mentioned. It's any kind of SO-- from rape and sexual battery to child molestation to statutory rape. That's a pretty broad swath.]