"Mom charged after gun found in kindergartener's backpack at school in Cicero" (she put it there!)

[Sancho]

18. No one would be preventing you from having a license to possess a gun...

...but we require licenses for all sort of things to prevent self-imposed danger (like to rent scuba diving equipment) or from danger to others (like buying certain chemicals).

Lots of licenses ask for background checks or interviews or references or medical clearance (airplane pilots).
In every case, your "rights" are only "limited" if you have an issue or problem that the process is designed to discover!!

I think everyone is assuming some kind of global psychiatric examination with a Rorschach ink blot test for a license - that is not the case. I can easily see something with a questionnaire (Have you attempted suicide?), a check on the truthfulness of the answers (Who are family, work, or friend references we can call?), a public record background check (arrest record), proof of safety training (approved gun course), a public media check (Facebook, Twitter), etc., etc.

This is not about your "general mental or emotional health". Nobody cares if you have text anxiety or you are seeing someone for marriage counseling, or you take valium before going to the dentist.

Many shootings involve untrained or careless people, but many are emotional or ill (at least temporarily) people well-known to the family, friends, schools, and coworkers around them as dangerous people who should not have easy access to a gun.