Most people, if you ask them, probably would say it IS punishment. Even some lawmakers agree. But the last time public registration was challenged all the way to the US Supreme Court, that court decided registration was NOT punitive. And at that time, it probably wasn’t. You mailed in an update once a year, and your picture was on the Internet. That’s it. But much has changed since then, and a new case must be taken to the Supreme Court to change that decision.