Occam's Razor? You think "The Pentagon did it" is the simplest explanation?
This did make me chuckle, Doctrine, but I agree with HoneyBadger. Previously suicidal pilots have had motives that were fairly evident on examination - huge debts being an obvious one, leaving out religious/political causes. Nothing known about these two suggests such an overwhelming motive. Depressed people kill themselves, not hundreds of others as well.
Occam's Razor prefers the explanation that fits the known facts with the fewest assumptions, no matter how unlikely it seems. "The pilots carried out a complex & carefully planned, homicidal suicide" looks like a bigger assumption than hijacking by a government to me.
The Razor is only a heuristic tool, though. And I doubt we'll ever get enough honest information to conclude.