Another scenario, discounting the alleged alien voices on the cockpit recorder, is that the Bush administration knew nothing of the 9/11 attack per se in spite of having been one of its causes, directly or indirectly.
After an improvisational period the administration realized that the attacks represented one of the greatest image-enhacing bonanzas a president could receive. (Hence Clinton's chagrin, and Bush's giddy "trifecta" remarks.) Foreknowledge is an interesting theory worth pursuing, because one could argue that the only worldwide beneficiary of the attacks was the Bush II administration and its closest circle of friends and family (e.g., the Carlyle Group).
Couple this with an all-oil all-the-time policy (supported by the former CEOs of Halliburton and Enron who set US energy policy) and within days the administration set its sights on... Alaska! Within the week, however, it was clear that the oil opportunity was not in a domestic wildlife preserve after all, but in central Asia.
The conspiracy theories flourish not because of an innate American paranoia, but because so many signal aspects of the administration simply don't add up. Fifteen of the 19 hijackers carry Saudi passports, but the "axis of evil" revolves around Iraq. Cheney's June 1998 speech to the Cato Institute refers to operating in "places where, all things considered, one would not normally choose to go. But, we go where the business is [i.e., central Asia]." There are dozens more easily cited facts like these that reveal, if not a hidden conpiracy's agenda, at least an ability to rationalize self-serving behavior ex post facto. The administration's repeated denunciation of any criticism as "unpatriotic" is, well, un-American.
The scent of oil mixed with defense contracting hangs over the administration's every move. If we "follow the money," the profiteers of 9/11 will turn out to be none other than those directly connected to the Bush dynasty and its grudge match against Saddam Hussein. An administration's conflicts of interest have never been quite so flagrant (let's not even talk about Michael Powell, today's poster child of self-interest in a public position).
What's the mainstream media's responsibility in all this? Profit concerns force you to look away from the real causes and real effects of the machinery of power, because they're far less photogenic. Besides, you're owned by the same people you're supposedly reporting on. That's why it's important for you to marginalize people who think in ways that conflict with what you broadcast. We don't all believe in "alien voices"; there are plenty of unintelligible remarks already emanating from the White House that you seem to ignore.