First of all, the facts: as far as we know at this time, all the disturbed man's firearms were purchased legally and FBI database background checks were done.  Next, regardless of any claims, a legal semi-auto can only fire 1 bullet per trigger pull, so there was no illegal modification to "fully automatic".  A person, with a little practice, can fire any gun quicker. Has anyone observed pro-pistol shooting competitions?  Has anyone seen a Wild West re-enactment, where the single-action Colt Peacemaker is "fanned" and 6 shots sound like a machine gun?  Next, it is also illegal for a mentally ill person to buy a firearm, the same as it is illegal for someone who uses marijuana or drugs to buy a firearm. Have any of these laws prevented any such mass shootings? A little research show a big NO on that. Laws are to punish the lawbreaker and that seems to be where there is some confusion on the left-leaning. Laws don't prevent crime, otherwise pot smokers would give up or not purchase guns.