Read some Schneier. A more accurate headline should be: "Nation on edge after an idiot demonstrates his idiocy". Nearly all terrorism has been performed by people who have serious mental deficiencies - even the 9/11 attacks depended on a lot of luck to succeed. Shit happens, but random opportunities usually aid the competent more than the incompetent. And nearly all criminals and terrorists are of lower intelligence, the few that are reasonably intelligent are seriously lacking in impulse control, which screws up their ability to make and carry through plans. Besides Bruce Schneier's work, see "The Bell Curve", and most newer literature on intelligence.