In the wake of Newtown, we are again debating the causes of these horrifying shootings. The usual villains are identified: Too many guns, too few guns, mental illness, a lack of prayer, a culture of violence and the general decline of American society.

Buried beneath this avalanche of blame is a deeper and more troubling truth. Our society celebrates revenge, and in the mind of an unstable, armed man, that ideal can become unthinkably tragic.

Our embrace of the nobility of revenge is not hard to discern. Retribution against those who have wronged the hero is the plot line of innumerable movies and television shows. For example, in the recent James Bond film, "Skyfall," 007 concludes the plot by killing his nemesis, who earlier blew up his place of employment back in London.

More pointed, perhaps, is the example of "The Dark Knight," a 2008 Batman film. Heath Ledger won (posthumously) an Oscar for his portrayal of the Joker, a villain who wreaks mayhem and death in Gotham City in retribution for the harsh denigration society had laden on a "freak."

In Aurora, Colo., at a showing of the film's sequel, a gunman shot at least 70 people. The man arrested, James Eagan Holmes, had dyed his hair to resemble the Joker's. Like the Joker, he extracted his own revenge through mass murder.

Our uplifting of revenge extends beyond movies. When Osama bin Laden was killed by American forces on May 2, 2011, spontaneous celebrations broke out across the country. President Obama and other Democrats raised the killing often, as a point of pride.

"General Motors is alive and Osama bin Laden is dead!" was one of the Obama campaign's applause lines. Now, of course, this revenge tale has been made into a major motion picture.

The problem with this broad celebration of revenge, typically lived out with a gun in hand, is that the message takes the shape of each person who hears it -- including those who are unstable, and who harbor deep resentments against their parents, their schools, society as a whole. Their target for revenge is us.

This seems to be especially true of school shooters. Seung-Hui Cho killed 32 people and injured 25 at Virginia Tech in 2007, leaving behind a note that condemned "rich kids" at the school.

Perhaps most famously, Dylan Klebold and Eric Harris mowed down classmates at their Columbine, Colo., high school after Klebold wrote that "My wrath ... will be Godlike."

Writing about these and other incidents, Frank J. Robertz noted in Scientific American that school shooters often build up revenge fantasies that are "buttressed by a distorted sense of what is just or moral, such as the need to avenge a perceived offense."

When a 20-year-old kills his mother, then slaughters innocent children, it is tempting to step back and say that we can never understand. That, of course, absolves us all of complicity in these recurring events.

The truth is that despite the complexity of causes -- and despite the ultimate culpability of the shooter himself -- we owe it to the memory of those children to think critically about our laws and culture to try to ensure that it will not happen again.

This is a moment to rethink our gun laws, our treatment of the mentally ill and the security of schools. But it is also a time to critically examine the deeply immoral emphasis on revenge that is rife within our culture.

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Mark Osler is a professor of law at the University of St. Thomas.