It was the dolorous stroke, the wound from which the US still bleeds, not because of the damage directly done by the airplanes or by Osama bin Laden's agents who hijacked them but for accellerating the authoritarian takeover that had been developing since the 1960s and was conspicuous already during the Reagan era in the 1980s.
About two years after the attacks, as we're already deployed in Afghanistan and are moving to invade Iraq, we'll discover that the US is abducting and torturing people, and soon after that there's a whole CIA program devoted to doing this, not because it produces usable intel but because some very rich people want some brown Muslim people to suffer for what those terrorists did. The whole thing is a pageant to white supremacy and punishing undesirable populations.
It was when I saw the true face of the United States. My whole childhood education had been a lie.