Hmmmmm....... Okay I'll bite. Just to clarify.
I think that the planes were hijacked and flown by members of Al-Qa'eda to their destinations. There are various reasons why I think that and not something else, but that's not germane to your question.
I think that the hijacking scenario is compatible with letting it happen, making it happen, or incompetence.
To be honest, I think that there was a mixture of people being told to leave Bin Laden alone, because he was still considered a useful asset, and a lack of vision. I also think that a lot of priorities shifted during the changeover between the Clinton and Bush administrations, and that a great number of things slipped off the radar. And in amongst all the bureaucratic manoeuvering, the significance of the intel pertaining to the threat was missed.
I'm far from convinced that NORAD did any less than it could that day, from my knowledge of the system, the flight times, and how the military works.
But can I prove anything? No. I don't have access. Neither does anyone else here.