It's currently rather difficult to deny someone a gun permit based on mental defectiveness. Something like .03% of the applications are turned down because of mental illness. They more or less have to have been adjudicated as such, not merely identified as a potential problem. Pretty much every mass shooting has been carried out by someone with mental illness, but they could still legally get a gun. Clearly, it needs to be simpler and easier to prevent people with severe mental problems to get a gun. But there's the rub, as Layout notes. The government would necessarily be involved, and that can't be good. They'll either mess it up, like they do everything they touch, or they'll abuse it like crazy, eventually declaring that everyone, other than government agencies, of course, are too crazy to own a firearm.