With respect to conspiracy theories, I always apply Occam's Razor:
"other things being equal, a simpler explanation is better than a more complex one."
IE, did the US government orchestrate a complex disaster, which would involve the silence/compliance of thousands of people
OR, did angry people from countries which we have had wars with, avenge their dead by attacking the World Trade Center.
I stand by the basic premise. Granted, many questions exist, serious questions, such as why Bin Laden's family was allowed out of the US when no one else was allowed to fly. But I do not necessarily believe that contradicts the main premise.
As Crocodile so adroitly pointed out (только если бы я умела так свободно писать по-русски!), evidence is needed for these conspiracy theories, before any of them can be taken seriously.
Occam's razor - Wikipedia, the free encyclopedia