Right now there are dozens, if not hundreds, of other "not previously seen to be unstable" guys out there buying guns...

Nope. Its much worse than that.

Thanks to the Marion Hammer, the NRA & ALEC, bunches of states, in addition to "Stand Your Ground" laws, have passed "shall issue" laws that permit convicted felons, domestic abusers, the documented mentally ill and all manner of other folks who shouldn't be allowed within 50 miles of a firearm, never mind a pistol, to to legally purchase & carry concealed weapons.

Florida is the most egregious case, but Colorado has a "Stand Your Ground" law on the books & may very well also be a "shall issue" state.

If ya ain't outraged, ya ain't paying attention.