I think we have to realize that Humans, as a species are no longer part of Evolution or Survival of the Fittest. With the Advent of medicines, it isn’t just the “Strong” that survive anymore.
I’m not saying that’s a bad thing! I’m just saying that we have to account for the fact that with each generation, the human species as a whole gets just a little bit weaker. And that certainly includes those with mental issues. Even more of a reason to have stricter controls over firearms.