Well, that goes a long way to explaining your reasons for your position.
But do remember for a minute, that we are talking about people who are prepared (coz they do it) to mass slaughter other citizens, destroy other cities. In the process of doing this to achieve their own geo-political ends, they are also prepared to allow US citizens in the guise of having a certain job (soldier) to be mass-slaughtered too.
Is it really such a leap of imagination for them to go from foreign citizens and US soldiers (citizens really, but just with a job title) onto american citizens who do other jobs?
But either way, you seem to be proposing (correct me if i'm wrong) that your disbelief the USG could do such a thing is stronger in influencing your thoughts on what happened than the evidence of the complete and total incompetence that this government must have indulged in.
That is no evidence at all sir! It is just showing us the limits of what you yourself can believe in. But we have the evidence of what didn't happen. And that is either down to history's biggest chain of incompetences ever, or down to someone making sure all emergency procedures didn't work. And to ignore the insider trading going on prior to the attacks. And to ignore the intelligence, quite specific, coming in from various nations, eg Pakistan, Sudan, Germany earlier on that year.
How can you equate such gross and massive incompetence across a whole spectrum of areas, being done by the world's only superpower?