When an abandoned building has a broken window, someone who would never throw a rock at an intact, occupied building may decide to break a second window. Once the building has lots of broken windows, someone might break in, steal all the copper pipes and light fixtures, use the place as a crack house and so on. Once it becomes known that the building in question is the home of squatters, drug addicts, and other interesting types there's a good chance that the neighbors will start moving away and customers will shop elsewhere. The downhill slide from there is obvious. The idea is to stop that first broken window by punishing the first rock thrower.
So what does this have to do with bullying?
When an adolescent is bullied in school and it becomes obvious that no one cares enough to punish the bully, other students participate or otherwise enable the bullying to continue. When this happens a relationship defined by fear, hatred, and a lust for revenge is established between the victim and the entire school community as a group. Sometimes this relationship grows to include the whole of society when the victim learns that bullies are coddled just about everywhere. The victim may initially become vandalous, then graduate to other, more interesting crimes simply because he's been taught to hate the civilized and child loving community he grew up in. This is apparently what developed prior to the Columbine Massacre.
So how do you discourage that first act of bullying?
School administrators, law enforcement personnel, and especially parents could begin stating in clear terms that bullies are criminals who belong in prison. It would also be wise to say very unkind things about enablers. If the bully is an athlete it would be very effective to boycott any event in which he is participating. Showing up and cheering reinforces the bully's sense of legitimacy and is a form of enabling. Adopting this as a consistent policy would undermine the bully's sense of legitimacy and its sense of security. It would also reduce the bully's parents' sense of legitimacy and discourage them from blaming the victim.
But don't hold your breath waiting for effective leadership to emerge. When it comes to bullying, the average person is some combination of mean, stupid, and callous. And as long as child loving people like Izzy Kalman and Frank DeAngelis are roaming the quiet countryside, bullies are safe from significant criticism.
And that, boys and girls, is why otherwise healthy, sane children become mass murderers in early adulthood.