Another simple example to use for the “not intended to be punitive argument”, which I have yet to see ever brought up.
Suggest that the individual you are speaking with, or one of their beloved family members, be placed on the registry for ten years. Or for the rest of their lives. And they have to walk the walk of someone on the registry in terms of travel requirements, living requirements, reporting requirements, the whole nine yards.
See how they react. “No! I/We/They didn’t do anything wrong!”
Your response: “And? It’s not punitive, right? Why does that matter?”
If you tell someone they have to be on a voter registry the rest of their lives, I’m sure they wouldn’t mind. If the sex offender registry isn’t punitive, then why would they object to being on it?