Raedwulf:

Even if you "weed out the emotionally unstable" etc., you are left with normal people, who, under the influence of certain stressors, can become emotionally unstable, even temporarily. If the weapon is at hand, and if it is as widely accepted as guns are in the US, then there will be tragedies, even following your "weeding out" idea.

Also, if you are a "normal," and have a gun in your house, does that mean that none of your emotionally unstable friends or family can visit?

The question isn't only ownership -- it's access.