Having doubled down on the Anything But Guns red herrings since Newtown, gun fetishists have shown a remarkable and unprecedented concern for America's mental health issues lately. The idea makes sense on its face; who would be in favor of crazy people having guns? Filter out the Crazies and you'll be left with only Responsible Gun Owners (and devious criminals, of course) owning America's private arsenal of firearms. The problems with the argument become apparent when subjected to anything beyond a passing glance. The only people who can be identified as "mentally ill" are people who have gotten treatment – voluntarily or by court order – and they're a lot less worrisome than the people out there who insist they're Fine and don't get treatment.
This argument is too tired to be interesting at this point, so it's pretty cool that we never have to have it again because it turns out that using mental illness as a criterion misses 99% of the people we should be worried about. According to a recent study, gun hoarders (six or more guns) are far more likely than the rest of the population to exhibit "impulsive, angry behavior." There is no single demographic profile that will cover all people likely to use guns to commit crimes, but it makes far more sense in terms of probability to stop focusing on Crazy and start focusing on Violent.
Because only a small proportion of persons with this risky combination have ever been involuntarily hospitalized for a mental health problem, most will not be subject to existing mental health-related legal restrictions on firearms resulting from a history of involuntary commitment. Excluding a large proportion of the general population from gun possession is also not likely to be feasible. Behavioral risk-based approaches to firearms restriction, such as expanding the definition of gun-prohibited persons to include those with violent misdemeanor convictions and multiple DUI convictions, could be a more effective public health policy to prevent gun violence in the population.
In short, if you're the kind of person who does things like punch people or destroy property when you get angry we should be much more worried about you having a gun than some college kid who's depressed. That's not to say that the latter is incapable of gun violence or the former is certain to do it, but as a matter of public policy aimed at reducing gun crime this would make far more sense.
Since when do our laws make sense, though. Especially when our Most Important Right is involved. It's far easier, legally and politically, to pick on Crazy People than to suggest that there's something alarming about good old-fashioned American male behavior like getting in fistfights and breaking things when angry.