"How does the all benevolent state identify the nuts who have no violent criminal history or treatment for mental illness without violating the medical privacy of everyone?"
In order to achieve the former, some people -- on the left and right -- would pursue the latter.
There have been people in the Disqus Era on these boards who have argued HIPPA needs to be made more lenient for law enforcement so that they can benevolently determine whether we are mentally unwell. For our own good, of course.