Certainly the Demonic Cabal which has been the controlling power behind both Democratic and Republican administrations since the beginning decades of the twentieth century, has no trouble thinking and carrying out the unthinkable:
to reconfigure the Middle East and establish a war-profiteering nightmare, resulting in 4,000 American soldiers being killed along with an uncounted number of Afghani and Iraqi civilians
In regard to 9/11, there are two main hypotheses, with sub-hypotheses branching out from them:
The Bush administration, the rabid right, and even some reputedly left-leaning liberals are warning Americans that any serious consideration of the hypothesis that 9/11 was a Bush conspiracy is a flight into lunacy.
However, even some sources within the Bush administration are now indicating the distinct possibility of complicity:
"A report released 6/9/05 by the FBI’s Office of the Inspector General raises new questions about the role of the US government in the terrorist attacks of September 11, 2001. The internal FBI study provides several important revelations about how US intelligence agencies ignored and even suppressed warnings in the period leading up to the attacks on the World Trade Center and the Pentagon that killed nearly 3,000 people." 1
The former chief economist for the Department of Labor during Bush's first term Morgan Reynolds commented in June, 2005 that the official story about the collapse of the WTC was "bogus" and that it is more likely that a controlled demolition destroyed the Twin Towers and adjacent Building No. 7. Reynolds said there is evidence that this was an "inside job." 2
"We still don't know by whom we were struck that infamous Tuesday, or for what true purpose. But it is fairly plain to many civil libertarians that 9/11 put paid not only to much of our fragile Bill of Rights but also to our once-envied system of government which had taken a mortal blow the previous year when the Supreme Court did a little dance in 5/4 time and replaced a popularly elected President with the oil and gas Bush-Cheney junta."
Bush administration did all it could have to prevent the 9/11 tragedy. The 9/11 Commission was a ploy to protect the Bush Junta from the people. The Commission
struggled against great obstacles put up primarily by the Bush administration, then issued a report that was a total coverup. In the early part of April, 2004, at least one poll showed that 70% of Americans believed Bush knew of 9/11 in advance. A June, 2005 MSNBC poll found that 94% of Americans believe Bush misled the nation in order to go to war with Iraq.
Even if you don't think that there's enough evidence to conclude that 9/11 was a Bush conspiracy, you need to:
None of us likes to think that our own government would deliberately carry out a murderous attack on its own people. But that hypothesis has to be given equal weight with the theory that the Bush administration was not complicit in 9/11. The Downing Street memo and related material now clearly show that Bush and Blair deliberately lied to their people to initiate the pre-emptive Iraq war. We need to consider all relevant sub-hypotheses in coming to an informed opinion.
In the coming years, you're going to have to respond to what the cabal does through its Bush and post-2008 puppet regimes. You can only respond sensibly if you have at least a working hypothesis about what's really going on in the world, 
including what you think happened on 9/11/01.
Intelligent behavior involves analyzing the problems and issues facing us to find an acceptable theoretical
solution which we then test in practice.
Once we outline the viable, relevant hypotheses, we must look at all the facts and see which hypothesis is supported with the preponderance of evidence. In trying to figure out the 9/11 phenomenon, we're not going to find many "smoking guns" (though perhaps you will find more than you might suppose at first glance).
My purpose in this essay is to provide a framework for thought in trying to make sense of the 9/11 terrorist attacks, not to review the evidence which supports or disproves the hypotheses and sub-hypotheses.
I encourage you to dare to think the unthinkable wherever it may take you. Don't let either right-wing reactionaries or pseudo-liberals frighten you from making up your own mind as to just what happened on September 11, 2001.
It's up to us to consider these questions as if our lives depend on them--because they probably do.

First posted: September, 2002 Last updated: 3/28/08
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1 FBI inspector general’s report: more evidence of government complicity in 9/11 attacks
2 WTC Collapse Due to Controlled Demolition, an "Inside Job," says Former Bush Advisor
Updates: