That's a touchy subject.
I'm not a shrink but I'm pretty sure that being depressed doesn't "automatically" mean you are suicidal or a threat to others. If a person IS suicidal then I guess it should be the doctors job to report it. That being said, there's ALWAYS someone who will abuse the system....like an anti-gun MDs. Most people speak with their MD about depression when, I feel, they should be refered to a psychologist for evaluation. Let a trained professional raise the flag. Sadly though, I'm sure you would have the same abuse of the system in the psychology world.
Read a few articles within the past few weeks that the CDC is getting involved in gun control studies.....again (tried it back during the Clinton admin). They will always use any method available to chisel away at our rights.
We all bitch that mass shootings are mostly mental health issues, not a gun issue, so it's kind of hard to defend against such laws. Crazies shouldn't own guns....period.