Ironically, you are concerned about civil rights but suggest the govt perform required mental health screenings on citizens??
Considering that most of the mass shootings appear to done by individuals with some form of mental illness, that most likely would require in-patient treatment and therapy....what is wrong with more mental hospitals and care if their personal doctors determine its needed?? Good grief you are on here calling for mental health screenings by the govt; what's wrong with more specialized care that would keep some of these deranged people off the street in the first place, before they kill others and in most cases themselves after?
It also appears many individuals seemed to "know" something was "off" (psychologically) with these perpetrators before the event occurred. Yet society now fears "labeling" these people as potentially "mental". Your position of now worrying over "civil rights" seems to reinforce that (unless the govt screening says so). Many of these shooters are acquiring or possessing the guns illegally prior to the time of the shootings (concealed, taking them from original owners, going into govt gun free zones, etc) anyway. None of your "new" law solutions would really prevent many of these specific shootings... unless they were to be institutionalized and kept out of the public in the beginning.