It is the prime justification
for the "war on terrorism" and the Iraq invasion.
If it can be shown that the attackers were not "Arabs
with box cutters", that the government lied to us, and that it was the
government that sponsored the attacks, then Bush and Cheney and
everything they stand for lose all credibility.
Just as you are probably used to saying, when someone
mentions Bush's "election", "Well, of course, he was not really elected
-- Gore and Kerry were," you should get in the habit of saying, when
"9/11" or the "war on terrorism" is trotted out as an excuse for some
government atrocity, "Well, of course, 9/11 was probably an inside job,
and the likelihood of being attacked by terrorists is less than the
likelihood of being struck by lightening."