The "why" question in post-Sandy Hook America most often comes down to two mutually exclusive answers: either too many readily available guns or too many mentally ill people. If we're not ready to accept the fact that both responses have significant elements of truth, then we're not prepared to address this most galling of societal problems.

The fact is, we have too many of both: As many as 300 million guns, including many that are better suited for the battlefield than the nightstand, and, by one estimate, 45 million troubled, delusional or clinically depressed people. Tragedy too often follows the mixing of the two.

Adam Lanza, who on Friday murdered 20 first-graders and the six adults who tried to protect them and others, didn't own a gun but tried to buy one in the days leading up to the tragedy. He wasn't denied because of some psychological profile that the gun store owner in that small Connecticut town was privy to. The sale was canceled because Lanza didn't want to wait the required 14 days. So he murdered people with guns from his mother's personal arsenal -- after first killing her.

We're still waiting to learn whether he was ever properly diagnosed with a mental condition other than Asperger's, an autism spectrum disorder not associated with violent behavior.

There's no question mental illness is a major factor in these mass shootings. "We have overlooked a critical issue, which is that at least half of the killers showed signs of serious mental health problems," The New York Times reported in a 2000 study that looked at 100 such attacks over 50 years.

"Society has turned to law enforcement to resolve the rampage killings that have become almost a staple of the nightly news," the study reported. "There has been an increasing call for greater security in schools and in the workplace. But a closer look shows that these cases may have more to do with society's lack of knowledge of mental health issues, rather than a lack of security."

The left-leaning periodical Mother Jones came up with similar findings in a more recent analysis published in November. Its title: "Mass Shootings: Maybe What We Need Is a Better Mental Health Policy." Mother Jones looked at 61 rampages over a 30-year period and found that "acute paranoia, delusions, and depression were rampant among them."

So, for as much as America needs to take another look at the way guns are sold, restricted and monitored, we need to look at mental illness, too. That's asking a lot of a nation so recently divided over whether health benefits should be extended to every American whether they want it or not. It's asking a lot of a nation that bats around women's health issues and medical access like a political shuttlecock. Now we're supposed to invest in more intensive mental health screening? Well, yes.

But declaring that underdiagnosed mental illness is the "aha" moment of this postmortem ignores that fact that mass shootings constitute a tiny share of the annual gun violence in America. Family confrontations and youth-on-youth violence in particular turn deadly when rage mixes with access to guns.

Solutions here are more complex than even these two factors. If there's something deep in the American psyche that produces these all-too-frequent spasms of horror, it's on us to root it out. The alternative is just too terrible.