Who is punished in a situation like this? A child that grows up never knowing their parent, or the parent that wants to see their child but isn't allowed to?
In my opinion, they both are. The child did nothing to "deserve" their punishment.
In the situation described in the OP, I would think supervised visits would suffice. Discreet supervised visits. However, I can't help but think that these visits would benefit the child more than the parent, since the parent can't really "parent".
In that situation, the child is no longer being punished even though the sex offender is. I also can't help but notice that the situation as described in the OP is far better than a sex offender wanting nothing to do with their child.
There are a lot of parents that do not want the responsibility of being a parent, and their children grow up into hurt adults.