that's why we have licensing requirements and databases that ensure compliance for such things as operating cars, trucks, airplanes commercial watercraft, etc...i.e. all things that could cause serious injury or death if not responsibly handled...so too of course with firearms...yet we see very ineffective measures being applied in that arena...
Moreover, there are no effective measures in place that can ensure that a person with psychotic tendencies but no history yet of mental illness/treatment from purchasing firearms that are exceptionally effective at killing large numbers of people in a short amount of time...i.e. "Assault Rifles"...if there are not stringently enforced restrictions on ALL gun owners, then the 'Psycos' will bea able to get and use them...given this fact of life, the prudent approach to dramatically reducing the horror and terror of mass shootings is to deny access to ALL citizens for those particular weapons. It isn't the perfect solution, but it has already been shown to be highly effective...let's at least do that...after all, there are still many other options for hunting, target shooting and home defense.
"