This is a sort of 'Life imitates Art' idea. It certainly makes you wonder about things like this. I've never seen that episode of South Park, but I was recently watching "
Armageddon" in the opening scenes where the meteorites hit New York City, always makes me wonder if some domestic terrorist saw this, wrote to Bin Laden and said, "hey, here's an idea...." Also the idea of using planes to attack building was written by Tom Clancy, in the book "Debt of Honor" where an embittered Japan Air Lines pilot flies his Boeing 747 directly into the U.S. Capitol building wiping out nearly the entire United States presidential line of succession including the President, most of Congress, nearly all of the Cabinet, the Joint Chiefs of Staff, and all nine Supreme Court Justices.