Thousands of people from the President down would need to be involved for the US government to have done 9/11. Not one person did anything to stop the attack, nor has a single person come forward, nor has any evidence been found. All this one an administration that leaked secret information like a sieve.
The buildings would have to be filled with explosives, all wired together (maybe by wifi!). This would take weeks if not months. People would need access to areas that would likely not be accessible. By the "theory" not one person thought anything was going on while people brought in and wired explosives all over multiple buildings.
Planes had to be flown into the buildings. Why? Why not just blow them up?
According to some "theories" the passengers were let off these planes and are still alive. Why? What would the point be if you're about to kill thousands of people?
According to some "theories" the BBC was given a script which they misread and announced one of the buildings had fallen before it had. This would mean that the BBC for some reason cannot be trusted to report on major events like 9/11 thus needed a script. It also adds to the pool of people who knew about 9/11 yet have said nothing for over a decade.
I honestly do not understand how the hell there is a strange conspiracy theory out there.
BTW no one has paid me to post this, but if you conspiracy nuts know someone who is paying people to post this kind of thing over the net, hook me up with them. I'm unemployed at the moment.