Anthony Hall is a man who is skeptical of the 'official conspiracy theory' of the cause of the events of Sept. 11 2001. He is right to be skeptical - that doesn't mean he is right.

http://www.salem-news.com/articles/october282010/scholarship-scams-ah.php

He seeks to demonize a defender of the official theory, Michael Shermer, and lionize its most prominent critic, David Ray Griffin:

"Michael Shermer’s approach to education marks a striking contrast to that of Professor Griffin. Where Professor Griffin seeks unrelentingly to speak truth to power, the largest part of Shermer’s oeuvre can be seen as an effort to flatter power, to serve power, and to cover over the darker side of power’s workings. In the tradition of P.T. Barnum, Shermer essentially acts as a new kind of intellectual circus performer, presenting psychological tricks and slights of hand as if these gimmicks were the outcome of genuine scholarly inquiry.

So if, like me, you honestly think Griffin's work is the most ridiculous nonsense you have ever read, you are a 'gatekeeper'. In some sections of American society, it is more socially acceptable to say it was an 'inside job' than to 'flatter power', as Hall puts it. If he had a good case, he wouldn't need ad hominem attacks.