Exactly.
If they don't slip through the cracks in the system as it is (like the AZ incident and the VT incident) and can't buy legally... they'll just get the gun some other way, or worse, build a bomb or something.
Step 1. Enact blanket gun ban.
Step 2. Molotov cocktails and machetes EVERYWHERE.
Step 3. ?????
Step 4. PROFIT!!!