I think this is a fact gun rights folks miss. We can clear people when they purchase guns, but a gun is a lethal weapon for years. You can't guarantee it won't fall into other hands in 30 years.
Some people argue we should give up, and embrace the number privately owned weapons in the US: http://www.theatlantic.com/magazine/archive/2012/12/the-case...
Others argue that registration of weapons is a better solution: http://swampland.time.com/2013/01/24/fact-check-the-gun-regi...
But the sheer number of these things is amazing. FWIW, the country with the second highest number of guns per capital is YEMEN. With a gun for only 5.4 out of 10 citizens. http://en.wikipedia.org/wiki/Number_of_guns_per_capita_by_co...
(IMHO, gun registration and improving our mental health system would go a long way toward addressing gun violence)