That's the wrong metric. There is no fool proof perfect solution to this problem, so holding that up as the benchmark will always result in any proposal missing the mark. Rather we have to focus on what will make a direct impact on reducing incidents like we saw yesterday in Virginia.
Last year there were 170,000 incidents of gun sales that were denied due to background checks that revealed the would-be purchaser was an x-felon, mentally ill, or had terrorist connections. I'm sure some of those 170,000 found a way to get a gun illegally - OR legally at a gun show but not all of them.
Your counter argument to my proposal makes some sense, but how about if we do this. If the licensing was done on a national level, a license could be revoked if the holder had a felony conviction or was determined mentally unstable. The license would be like a credit card with a magstrip or chip that can be swiped for instant approval - or called in (again like a credit card transaction).
The bottom line for me is that we can't just shrug our shoulders when there is another senseless killing and say "$hit happens don't mess with my 2nd amendment rights" That's a cop out. WE can protect gun owners rights and do a much better shop of filtering the access at the same time.
Theres no way id trust the government to monitor convictions or mental health records. Some incompetent government employee is the one who incorrectly entered the data which allowed the Charleston shooter to buy his gun. It would be ok in a perfect world, but not in a real one.
Lets look at the current laws and remember this is a constitutionally protected right. There isnt one shooting that wouldve been prevented. All, except the aforementioned Charleston shooter, had little/no criminal history and little/no history of mental illness.
I think one item that goes unmentioned, is the media unintentionally creates a worship subculture for this type of behavior. They shouldnt mention the shooters name, show their face, or share any of their social media psychobabble. If these people thought theyd be dying without everyone remembering their name; it would go a long way towards stopping these.