The world trade centre attack wasn't planned or allowed to happen by some secret cabal.................but when it did happen, I bet Rumsfeldt, Dick Cheney, and the rest of their chums thought it was bloody christmas- saved them years of building up a new enemy to protect folks from, and all the excuses they'd ever need.
Most conspiracy theories rely on a level of skill and competency unattainable to these types who surround themselves with yes men!
How do YOU know it wasn't planned
I doubt if some of the terrorists were out on in picnic and thought, 'I'm bored, let's go to the airport, pinch some planes and kill ourselves by flying them into some big buildings.'
There had to be planning of some kind. Another conspiracy theory to be mulled over for years to come. I wouldn't put it past the CIA to do it though, after all fear is control. Keep people scared enough of the bad guys and you can control them through the fear