Really? You rather that about 3 million of these are left on their own then? You mean you would rather that another Ted Bundy or James Holmes is left out there stewing in their demented mind?
There is most likely no way we could cover all..but is it worth it if we cover just one? I want you to go and ask the survivors of that killing if it would be worth it.
This used to be covered under local county administration. You are against that too?
The simple (and all too simplistic) answer is that anyone who cannot be trusted with a firearm, whatever the cause, be it criminal behavior or mental defect, should not be running around loose. But confining them all is too costly.
On the other hand, having everyone who desires it armed and trained makes it likely that the damage inflicted by the miscreants will be minimized by those around them.