I believe this is one of the fuzzy areas of law. By having the state do it, they meet some of the outcry for such a registration; without such justice, there would be greater approval for more extreme tactics done with the aid of the internet.
My concern — and this doesn’t rise to cause to oppose such registration — is that there is often little distinction made between levels of offense: to the public, a “sex offender” is a “sex offender” is a “sex offender”: a peeping tom is no different than a rapist. And how natural is it to fear that the guy busted for being a peeping tom is really a rapist! But it’s also natural to fear that a burglar is a murderer, yet we don’t presume as a society that a burglar is a murderer and punish his as such.