Why do so many young Palestinians and Israeli Arabs—some of them, by all accounts, normal and happy and well-balanced people from loving homes who drive nice cars to good jobs—suddenly take to the streets and perpetrate mad acts of violence?Here’s another way to ask the same question: Why do so many young Americans—some of them, by all accounts, normal and happy and all that—suddenly take semi-automatic weapons to school and shoot up their friends and teachers?The answer, it turns out, is simpler than you’d think. Writing in The New Yorker this week, Malcolm Gladwell argued that the answer may very well be merely the existence of an appealing precedent that invites even the unlikeliest of subjects to join. This idea is based on the research of Stanford sociologist Mark Granovetter, who looked at inner city riots and tried to ascertain why so many people you’d never think were prone to violence would suddenly decide to join in on the mayhem. The first person to pick up a brick and smash the store window, Granovetter found, was a special case, a maniac with no compunction. The second, however, is not: he or she is likely swayed to riot based largely on the fact that one person had already gotten things in motion. By the time you get to the hundredth person, you have more or less normative folks who are just partaking in what, by then, is a social activity with its own affirmations and traditions.While the many teens who shot up their schools had nothing in common—some were abused as children while others were beloved and nurtured, some were poor while others were rich—they all shared an admiration for the school shooting tradition, which was set in motion by Eric Harris and Dylan Klebold, the perpetrators of the massacre in Columbine. The post-Columbine shooters dressed like Harris, talked like Harris, even timed their attacks to begin at 11:14, the same exact moment he first fired his rifle. They were just following his lead.Whose lead are the young Palestinian stabbers following? That, too, isn’t a complicated question. They’re following the Facebook posts that tell them that serrated knives are better than smooth-bladed ones because they cause more damage to internal organs, or pages with titles like “Mobilize for the Third Palestinian Intifada” that urge them to go and attack; they’re following the cartoons posted online that show young and heroic Palestinians slaughtering supine Jews, with blood spurting for effect; they’re following Twitter hashtags like #stab, which shows where in the human body one should aim for easy entry, or #poisontheknifebeforeyoustab, which is pretty self-explanatory.How many of the young and impressionable men and women who see these messages actually pick up a screwdriver or a vegetable peeler and seek innocents to impale? Just like school shooters, the answer is a tiny percentage. But a tiny percentage is more than enough.And the tiny percentage is likely to grow. On Friday, I wrote about a young Israeli-Arab woman who attempted a stabbing in the northern city of Afula despite being a divorced mother of a small child and a graduate of the Technion, one of the finest academic institutions in the world. Recent Israeli media reports suggest that the woman, Isra Abed, may have been motivated not by any ideological force but by deep mental problems; taking a knife to a public place may have been her elaborate attempt at suicide.There are many more like her: the mentally ill, those mocked at school, those confused about their identity, those mad at the world for not recognizing their true value, those rejected by a lover or ignored by a crush. These are all normal archetypes every society has aplenty. But when your society starts singing the praise of murderous violence, when authority figures state publicly that violence is good and holy, things get that much more toxic. Imagine if the Democratic and Republican parties, Barack Obama, Fox News, and Rachel Maddow all agreed that school shootings were glorious American acts, and that the shooters were going to heaven. Our school shooting problem, which is already pretty awful, would probably be many, many times worse.This is what we’re seeing unfurl in the West Bank. When every aspect of your life—from the words of your president to your Facebook feed—praises murder, you’re given something more profound than merely a call to action: you’re given a club to join where you can finally fit in. Shutting it down is going to be very hard to do.