Because it is just silly, for starters. Yes, a missile was used to hit the Pentagon! And all of those hundreds of civilian witnesses in the DC/Viriginia area who witnessed a plane hit the Pentagon, they were just seeing things? (I lived in the DC area at the time, and I know a couple people personally who did witness it). The stuff about the WTC is equally nutty.
Aside from this, is there some reason to think it would be implausible for a group of militant Islamic fanatics to plot and carry out such an attack? Frankly, that sounds like something that would be easier to carry out, esp. w/ the suicidal proclivities of some of them, than would some Tom Clancy-like conspiracy on the inside.
I find it mostly to just be a big, unnecessary distraction from identifying the BS that's being perpetrated NOW by the Bush Administration, and putting in the efforts to stop them. I think the theories have been solidly debunked for some time now, and not by Bush Loyalists, either.
That said, the best stuff that I have read about the Bush Administration and 9/11 was this 4-part series:
http://www.wsws.org/articles/2002/jan2002/sept-j16.shtml
What's said in that series of articles is about as close to conspiracy-theorizing as I will get (I appreciate the articles more for the thorough breakdown of many facts pertinent to the 9/11 attack).
What is more critical at this point, I believe, is if it would be possible for the government to attempt some sort of "inside job" attack to help further consolidate their power. While I would not call it "likely" I would say that it's a distinct possibility, and one that woud certainly not be out of the question for the Bush Administration. Certainly there are PLENTY of right-wingers who relish the idea of another attack, precisely for that reason (to justify the near-elimination of democracy in the US, for the stated purpose of our "safety"). Indeed, there are those who hope and/or pray for another terrorist attack in the US, and they are not always afraid to say so openly, and when they do, the "liberal-biased" media - ever fearful of being labeled "liberally-biased" - will give them a platform for such (treasonous?) insanity. Case in point, this guy who just recently said "we need another 9/11":
http://www.philly.com/dailynews/col...___To_save_America__we_need_another_9_11.html
Lastly, those who haven't seen this (very short - 82 secs.) clip of Dick Cheney in '94, talking about going into Baghdad would create a massive "quagmire", should do so - it's a must-see, a real jaw-dropper:
http://www.youtube.com/watch?v=6BEsZMvrq-I
Thanks for hearing me out....