Before we launch world war 3, ask yourself: would you care if Iran, China and Russia were really behind the attacks?
Of course you would.
Well, then you would also want to know whether Bin Laden was really behind 9/11, whether rogue elements within the U.S. allowed the attacks to succeed, or whether it was actually an "inside job".
Think about it. If, like Howard Zinn, you say "I don't care if 9/11 is an inside job", you are really saying you don't care if future attacks are real attacks or false flag attacks intended to justify war against a concocted enemy.