There are some fishy things about 9/11, but the controlled demolition theory is absurd. At worst, the gov't knew about it and let it happen. Most likely though its more like the gov't had intelligence but failed to act on it in time. Sometimes you just have to consult Occam's Razor. It's simply too contrived for such a grand conspiracy to happen in the information age. The Kennedy assassination, on the other hand, was almost certainly a conspiracy.