I'm opposed in general to the wide availability of firearms in the civilian population. But I was scared out of my teeth during this background checks vote. And it's a topic that's bound to return, and is as morbid a reality as it gets for the mentally ill.
To the facts. There's no generally agreed-upon definition of "mentally ill" as a legal matter; competence is judged on a case-by-case system with the support of medical specialists. On the other hand, the medical definitions of mental illness (ICD-10, DSM-IV) are expansive and wide-ranging, because they serve the need to treat, not the need to exclude and marginalize. Trichotillomania, the habit of pulling hair out when stressed out, is counted as a mental illness. So is anxiety and depression.
You may argue that the filtering of firearms should target so-called "serious" mental illness such as bipolar disorder and schizophrenia. The problem is that there's no real scale of "seriousness", nor is a clear correlation between severity of certain symptoms and propensity to violence. All-out fried up schizophrenics may not have the judgment to plan a proper attack the way someone who has a bit of anxiety has. In actuality, while recent cases of inexplicable, gross violence have been pigeonholed into this or that medical diagnosis, no reliable source ever emerged, nor there are reliable correlations between ICD-10/DSM-IV diagnoses and criminal behavior.
Is this an issue of civil liberties? I hate that term, but it is -- we either set the same free-for-all chaotic conditions for all citizens with no criminal antecedents, or we establish a comprehensive gun control framework. My personal take is that individuals shouldn't be allowed more than a six-bullet revolver and a small allowance of munitions; that's enough for the kind of small-scale deterrence that civilian weapons can ever have. Hunting weapons belong to hunting grounds; they should be rented at the places were hunting is allowed and stay there.
The actual problem, however, is the unsealing of medical record. The very way America wants to frame mental illness to let firearms off the hook for firearm violence is diagnostic of a pervasive pattern of stigmatizing mental illness and the mentally ill in pop and folk culture that could be compared to how blacks were once said to be particularly prone to rape. For one, as the culture stands now in the western world, disclosing a mental illness in the workplace is very problematic. This is not a matter of laws only, which have been sluggishly advancing, but of the continual repetition of incorrect assumptions about how mental illness works and what's the extent of accomodation that the mentally ill really need. As a result, the mentally ill either go "stealth" -- and you can find them anywhere in the hierarchies of power -- or go "under", sometimes unable to exert enough judgment to keep in the treatment that would make them "sane" enough to work the kinks of social security and transient work.
I've been chatting with other mentally ill folk these days, and there's rational fear of widespread profiling. What happens when they decide mental illness is a terrorism hazard and the MI are added wholesale on the no-fly list? No one ever contests the no-fly list, and yet it's something that can ruin someone's livelihood, depending on what they do. (Standup comics, for one, live in fear of the no-fly list) At such a point, the stigma stops being "just" a matter of liberty, equality or dignity. It becomes an impediment to the pursuit of happiness. And doing this to the very people who have to fight to hell and back to keep their stuff together and keep moving forward is as morbid as it gets.