Unwarranted Surveillance Quotes
For the classic formulation, see Brandeis, Olmstead v. U.S., 1927
The register was originally created so that people could be warned about the pedophiles who had served their prison time and were now living in a community. They are also banned from living close to schools, parks and other locations where children might gather. Then rapists were added. This in turn covered statutory rape. And that covered an 18 year old having consensual sex with a 15 year old who may have lied about his/her age.
The state of Michigan was trying to require adult welfare recipients to undergo random drug testing while adults not on welfare had the Constitutional right to be tested only if there was some reason to suspect them. See for a reaction to the case.