Those terrorists broke the unwritten rules of airplane hijacking. Before them, hijackings involved forcing a plane to fly to somewhere, some number of political demands, negotiations with governments and police, and generally peaceful resolutions. What the 9/11 terrorists did was awful and horrific, but I also recognized the ingenuity of their hack. They only used weapons that were allowed through airport security, transformed civilian jets into guided missiles, and unilaterally rewrote the norms around airplane terrorism.
