Controlled Demolition is the dumbest conspiracy theory I've ever heard. It can only be believed by folks who have never so much as planned a birthday party.
I once watch a National Geographic special ( fairly certain it was Nation Geographic ) on the Twin towers back in the 90's.
The premise was how the World Trade Center was like a small city and what it took to run it.
What was interesting was they talked about how the towers were designed and they pointed out that they were designed to fall into themselves if they had been so damaged to a certain point.
I think in the end though, there was a conspiracy that led to the Towers to fall, but it was a conspiracy of incompetence.
Led by Jamie Gorelick the Towers fell due to typical government incompetence, preservation of fiefdoms, and bending backwards for the PC crowd.
The real tragedy was the whitewash of the 9/11 commission and our Federal and State athoridies being unable to learn from history.
In the end AlQada won, because now we are the suspects to be watched and patted down.