They do bring up a good point, and that is mental illness (one common thread here, and a very likely source for these things)
The problem becomes even bigger then, though.
Different than some might think, mental illnesses are not a lifetime stable event.
Around 10% (yeah, you can read that again) of the population experience a schizophrenic episode in their life.
Manic depression, Depression, paranoid delusions, etc, etc...
Would have to be added to the list.
Also the general, more vague idea of "unstable" or "irresponsible".
Fun fact:
A lot of men in jail for violent crimes have been assessed in a study and found to be suffering from a borderline personality disorder.
http://law-journals-books.vlex.com/vid/borderline-personality-disorder-distinct-317030982
http://en.wikipedia.org/wiki/Borderline_personality_disorder
This is extremely disputed, hard to diagnose and has a lot of overlap with culturally accepted tendencies in some circles
(as in Alex Jones fits the bill quite well)
So..
Who'd like to be screened annually?
And what will you do when the shrink labels you unstable?
Give up your weapons until the next appointment?
And - do we give weapons back to people once diagnosed like this?
The other question is that of a criminal background.
What do we include in that?
Only violent offenses? Might be too late at that point.
Drug use? (Helloooo, marijuana users)
DUI?
Theft?
Where do you draw the line?
::emp::