In functional families and communities people know who has a gun problem...

... and they discourage it.

People who behave foolishly with guns are in the same class as drunk drivers, they are very dangerous to themselves and others.

Healthy family, friends, and community have no problem taking the car keys away from someone who is drunk or otherwise unfit to drive, and the same ought to be true of guns.

If the second amendment prevents federal intervention, then friends, family, and community can still intervene.

Potential mass murderers are readily assimilated into a gun culture that fantasizes about murder in their gun play. This same culture is then shocked when a few of their own turn the fantasy into reality.