Keep in mind that the term "Sex offender" is an incredibly broad term, and all the negative connotations that are attached aren't necessarily warranted. What about the 18 year old boy who gets caught having sex with his 17 year old girlfriend? Press charges, and he's on a list, and you're horrified he's living in the same building. "Sex offenders" are painted with a very wide brush, and for every sicko who gets off on luring little kids to their ruin, there's four college frat guys who were dared to moon the local sorority on parent's night. These are the kinds of things that are called sex offense.
Recidivism is an interesting occurrence. Generally, the chance of returning to a crime decreases substantially when the perpetrator has a strong support network helping him stay clean, as it were. How many support networks are there to help some guy who did a horrible thing, that he can't ever erase from his memory, and can barely stand to live with how he hurt some family? He doesn't want to do it again, but he doesn't know how to stop. He doesn't know how to stop because whenever anyone finds out what he did, the immediate and universal reaction is one of utter revulsion.
I know it's not nice to contemplate, but good people can do horrible evil things, just as horrible, evil people can do very good things.