In order to prevent yet more tragedies like the shooting at the Planned Parenthood centre in Colorado Springs, gun rights activists – and rightwingers in general – often suggest that we need to prevent the ‘mentally ill’ from gaining access to firearms. In fact, even Democrats and centrists say that, “I think as a state, but as a country, we have got a lot more thinking about this, of how to make sure we keep guns out of the hands of people that are unstable,” as the governor John Hickenlooper said (and the Mayor of Colorado Springs, John Suthers, echoed).
This strikes me as one of those anodyne statements that is simultaneously impossible to disagree with and yet completely useless. Of course we should be tough on the causes of crime. Of course we should improve our children’s education. And of course we should prevent those who we think are likely to kill civilians with guns from possessing guns. The question is how we do that.
Robert Dear, the man suspected of the Planned Parenthood killings, was considered to be strange, not dangerous. He had no entry in any database that marked him as being mentally unstable – because no such database exists. It’s hard to imagine how one could ever exist; the notion stinks of Precrime-style profiling, an attempt to predict crimes that haven’t yet been committed. Mental illness is not a crime, and the great majority of people who are mentally ill (a woolly category if I’ve ever seen one) do not commit violent crimes. And even if that were not the case, science is yet to produce a foolproof ‘mental illness’ detector.
I realise that the whole ‘guns don’t kill people, stop mentally ill people from getting guns’ is essentially a smokescreen. My point is that it’s a terrible, incoherent smokescreen. Gun rights activists love to cite the US Constitution, but I can’t think of a worse violation of it than a law prohibiting individuals who’ve been designated as ‘mentally ill’ from ever possessing arms. What if Obama designates all gun advocates as being mentally ill?!!?!!11!
mssv 
This might be what Bruce Schneier calls a “Movie Plot Threat”.
There need not be some centralised Orwell-esque central database of “people deemed too unstable to own a gun” – ineffective as it would be given that, as you point out, someone like Robert Dear wouldn’t have been on such a database anyway.
However, it might be sensible to adopt a pragmatic approach as we do in the UK. When you were to apply for a Shotgun or Fireams Certificate in the UK, you pass your G.P.’s details to your local police force, along with your permission for them to contact your GP should they so wish. I don’t think it is yet mandated, but many forces will contact your GP to check you have no medical history which would suggest you might be a danger in possession of a weapon or ammunition; and will further ask the GP to make a note on your medical records that you are, or might be, a gun owner – such that if you have a change of medical circumstance which might lead to an issue, the GP can consider suggestion you should re-consider your Certificate holding, or contact the police directly.
Same net effect as a database, but without the hassle; and probably more efficient too.
Whilst there’s certainly an argument to say that your medical records and situation should remain private (and that you should be able to see a doctor in confidence), it is perhaps not a wholly unreasonable trade-off: you want to own a gun, you give up a small part of your freedom for the privilege of being allowed the access you want. I certainly think that’s a reasonable trade for a hobbyist, although whether that is entirely fair for someone who’s work requires a gun (pest / vermin control, farmers, forestry, etc.) is another discussion.
Of course, it doesn’t help if somebody becomes unstable and doesn’t seek help; and most gun crime is committed with unlicensed weapons anyway (those with Certificates tend, on the whole, to be exceptionally law-abiding folk; one wrong move even in something unrelated, and that could be the end of your ticket), so it’s not an answer. But perhaps a sensible precaution for the handful of cases it might prevent turning sour by picking up on early warning signs of a deterioration of mental health.