I am horrified by what happened in Newtown, as anyone would be. But I am a policy analyst, with some specialization in counter-terrorism - which has some overlap. So the only thing I know how to do is consider and evaluate options. I do so with humility. We must do something, but it would be best that whatever is done is more than symbolic and also effective. Politics, and hence policy, is the art of the possible.
There are appear to be three basic approaches, which are not mutually exclusive. The first is to reduce the availability of guns, the second would be to harden the potential targets, and the third option is to attempt to detect possible mass shooters before they act. There are no magic wands with any of these options.
Undoubtedly there are prudent, reasonable gun control measures that could be adopted and that would reduce the ability of bad people to get their hands on deadly weapons (Emily Bazelon in Slate outlines some approaches). This is all to the good. The details of gun control are beyond me, but the obvious point is that there are already hundreds of millions of guns in circulation in the United States. Programs may reduce that number and better regulate them - but this will be at the margins. There will still be enough guns (and ammunition) "out there" that determined malefactors will be able to obtain them. Aggressively pulling guns out of circulation will require large-scale intrusive and coercive government action that is not politically realistic and would probably have other consequences that would not be good for the country.
One example is Australia's mandatory buy-back program after a 1996 mass shooting. But at the time there were about 3 million guns in circulation in Australia (one for every seven Australians.) The ratio in the United States is closer to one gun per person. Enforcing mandatory buy-back program for certain classes of firearm on that scale would either require extensive major law enforcement operations or would become an unenforced law. Either path is problematic.
(For a look at the challenges in preventing suspected terrorists from obtaining firearms, see this interesting report from the Foundation to Defend Democracy, co-authored by Daveed Gartenstein-Ross.)
None of this is to say that reasonable gun control measures should not be undertaken, only that there are limits to what they can achieve.
Another response is hardening the targets. More than a few observers have noted that had there been an armed security guard, it is highly probable that the Connecticut incident would not have occurred. Probably true, but there are a great number of potential targets (we've recently seen movie theaters and malls shot up as well.) Even if we limit protection specifically to schools, there are thousands across the country - do the resources to provide this kind of security exist?
One response to avoiding the cost is the classic libertarian argument that more people should be armed. This may not be a fruitful path. The libertarian argument is that an armed society is a polite society. Maybe, but I have a bit less confidence in human reason. While armed individuals might prevent these massacres, but there would be a corresponding increase in disputes escalating to gun-play. Also, from a personal perspective, this means I have to carry a gun - or risk being at the mercy of those who do. I frankly don't want the responsibility, I'm quite happy to outsource public safety to the police.
There may be other methods of hardening the targets. Increased school preparation for this kind of scenario may save lives and physical security might also be deployed. Finally, there may be creative ways to get responsible individuals who are licensed to carry firearms into schools. Could room be made for retired police officers and military personnel to become teachers? This seems like a potential win-win.
Assuming offering blanket armed protection to all schools is not realistic, could smaller scale steps improve school security? This would not be as dramatic, but might be more practical.
Screening for Possible Murderers
There has been much discussion about improved mental health screening to prevent these kinds of incidents. As with the issues discussed above, this is hardly a panacea. Also, first and foremost, we do not actually know anything about the mental health of the shooter. Everyone on the internet is assuming some sort of mental illness, but these are arm-chair diagnoses.
That being said, improving mental health access and efficacy would be a very good thing. But mass mental health screenings would be problematic. Just like in screening for terrorists - there would be a great many false positives (probably far more than true positives), and false positives are expensive. A person falsely labelled might have their life ruined or might sue, embarrassing the responsible agency. In addition, this too might be a path to a deeply coercive and intrusive state.
The appropriate policy response would probably be to provide substantial grants both to existing mental health programs and for more research on the issue. But a useful additional area of study might be the legal aspects of mental health. Careful studies of how to balance the competing priorities of freedom and public safety in regards to the mentally ill would be very useful. This is a great challenge since, by its nature mental illness hampers the ability of those who suffer from obtaining help, but allowing the state force help on the mentally ill is a power that can be abused. Further consideration of these issues may help contribute to the more effective delivery of treatment to those who suffer mental illness.
Quite simply, there is no realistic policy just sitting on a shelf that would guarantee such massacres do not occur. But there are many more modest policies that could reduce the likelihood of such massacres - they are well worth pursuing.