Why? Alienation is such a built-in part of our society (and I mean our global society, unless you happen to live in some enchanted rainforest where people actually still give a damn; the US is only the worst offender) that we should just take things like this for granted. While you're watching the coverage, take a moment to reflect during a commercial. Try one where a pimply kid is generally scorned and ridiculed until some product fixes his complexion. Or one where a working mother is hassled mercilessly by her family until she discovers some kind of miracle convenience food/food service, whereupon she is loved again. Think about the messages that we're constantly bombarded with. Don't watch much TV? Think about it in church, then. Just let your mind wander while the appointed religious authority is screaming/droning on about how you're worthless and doomed unless you recite a particular set of words and cough up a portion of your income.
Some people still seem to wonder why every few months we get a fresh body count from some kid cracking under the pressure.
The finger pointing and blame-shifting are all part of the picture, too. Marilyn Manson made 'em do it. KMFDM made 'em do it. Violent video games made 'em do it. The internet made 'em do it. Sure, whatever. Anything but a cultural phenomenon we all share, or at least allow to continue.
Or maybe they were just "that type". You know; angry, oddly-clad teenage boys with secret agendas. Unlike every other teenage boy anyone's ever known. Surely Mr. and Mrs. Joe Schmoe's darling little boy would never get angry, dress so as to stand out from the crowd, embrace rebellious music, identify with a subculture, or harbor weird fantasies. Oh, no. How could they NOT have known by the trenchcoats and quasi-goth music that those guys were secretly building bombs?
So now we get to be suspicious of "that type". Goths will get a little more notoriety because nobody can seem to tell one trenchcoat afficianado from another. Life just got a little harder for the sensitive teenager, and a little fatter for CNN's pet child psychologists. We love easy answers, and this one is easier than most: Your kid has a trenchcoat? Listens to music with aggressive overtones? Get him to counseling. They'll give him drugs. Problem solved. (Hmmm.... Wait a minute... Y'know... "HEY MOM? WHERE'S MY MARILYN MANSON CD? IT WAS RIGHT HERE IN MY BLACK TRENCHCOAT!" Heh... What's Prozac going for on the streets these days?)
I'd like to suggest that while we're worrying about "that type", we also worry about a few other "types":