Funny story there: I was stuck with a conspiracy-minded high school teacher who insisted that some sort of flash lower down in one of the towers was proof of a demolition. I got fed up with listening to it each day, so I calculated how long it would take a shock wave to propagate through steel, from the crash site to the flash below. It pretty much worked out.

Considering how many surveillance laws were passed in the USA after 9/11 (independent whether it was a terrorist attack or some controlled demolition) and wars were started on Afghanistan and Iran (the latter having nothing to do with Al-Quaida or the attacks on 9/11), it should be obvious that at least from the political side there is/was a hidden agenda:

- Conspiracy theory view: Some buildings were demolished. Politics seizes the opportunity to pass surveillance laws and start two wars.

- Non-conspiracy view: Some terrorist attack event happened (but every actuary can give you estimates on how often such an event is to be expected, so nothing surprising here), so politics seized the opportunity to pass surveillance laws and start two wars.

The only difference between these perspectives is what happened the three towers and some part of the Pentagon building to collapse.