Ah, but they did! The U.S. economy was shut down for several days and it was in recession for a long time afterwards. Look at the airline industry. Look at the U.S. response. While I think there is a remote possibility that officials in the U.S. government knew about the attacks, the left has adopted the wrong analysis of the attacks. They have adopted a racist analysis that relies on this crazy idea that the U.S. government carried out these attacks. This makes all of us look bad. What's more, it has turned into a dogmat where people who share my take are seen as heretics.
9/11 showed how vulnerable the U.S. governmnet is. We should seize that as encouragment to press forward with even more radical social changes.
Chuck