That's a fair point. But with respect to, I guess, the heart of your question--whether too much focus is being placed on the privacy rights of the offenders, and therefore, by definition, you've built in failure--I'd go back to the point I made earlier. It seems to me that a huge amount of information is already collected about the offender; I would ask what additional information you're proposing to add.
If there are problems with respect to police agencies not being able to access this, or if the system is structured in such a way that it's not easy and quick to search the registry, then by all means make those changes. The worst possible case would be to have this information, to intrude on the privacy of the individuals by collecting this, and then have a system that doesn't work.
You either make it work, preferably by measures that are as least intrusive as possible, or come to the conclusion that, by the very nature of the offences, this type of registry is not going to work.