I would think flooding the market would only aid business and the economy. After two years, the gangs, cartels, and mobs will have them whether such a law is in place or not, while mass murderes who snap one day, on the other hand, won't be able to go to the store and buy them.
Since when has making a thing illegal stopped anyone from procuring the illegal thing in question?
Gangs and the mob won't sell these illegal items in question? Which motivation will have the greater effect? The way their moral compass points, or because they don't like money?
Our most recent mass murderer had been working on his plan for months, by the way, as most of the mass murderers have, as opposed to "snapping one day". They seemed to find the time to write journals, lists, schematics, stick-figure drawings and manifestos. Seems to me like plenty of time to locate and purchase anything they could afford, provided to them by by a vendor whose only requirement for transacting business is that the purchaser is in possession of cold, hard cash.
Va. Tech
Columbine
Oklahoma City
1996 Olympic Games
Jack the Ripper (No gun, by the way)
Just to name a few...
Your gonna need this: