"The registry is not considered punishment ..."
Some people consider execution to be humane because it puts the convict "out of his misery." You commit a horrible crime and are sent to prison as a punishment. Once you've served your time, and have completed your parole, why should the punishment continue because being restricted to certain areas and being excluded from certain places and unable to find a decent job is indeed "punishment."
Somebody who has physically attacked others with a club or knife or gun are allowed to live where they want, even though they are the criminals most likely to offend again, so what makes them different?
I can walk out of my house and kill somebody, but once the punishment is over I can go wherever I please and the only stigma is having a prison record because nobody will see my name and face on a state-maintained database for the rest of my life.