"...you find it easy to believe a handfull of people with box cutters can fly a bunch of planes into some buildings!"

Yes.

The plan was elegant and simple.  It did require preparation, including gathering identifications and passports, and learning the basics of flying a large aircraft (but not how to take off or land).  They needed enough money for flight school, travel, and living expenses.  And box cutters.

It was simple, do-able, and they did it.

All I'm asking for is some credible evidence for a broader conspiracy reaching into the White House or (name your agency here).

With all of the backstabbing going on by members of the previous administration and the Republican Party in general, if there was any such evidence, I think it would have come out by now even if it didn't during the 9/11 Commission's investigation.  But the only people who are talking are people whose sole occupation is selling their hollow books (see Alan Miller's comment below), and no one is vouching for them.

Besides, why hasn't Richard Clarke talked about any of this?  If there was anyone credible who could have direct knowledge of such a conspiracy as well as a motive for exposing it, wouldn't it be him?  Or is he "in" on the conspiracy?

And yes, before you hang me for it, I admit that is another "lack of evidence" argument just like so many of the conspiracy theories.  But the positivists always bear the burden of proof, and lack of evidence is sufficient grounds for dismissal, not acceptance.