'You did this hit piece because your corporate masters instructed you to. You are a controlled asset of the new world order ... bought and paid for." "Everyone has some skeleton in the cupboard. How else would MI5 and special branch recruit agents?" "Shill, traitor, sleeper", "leftwing gatekeeper", "accessory after the fact", "political whore of the biggest conspiracy of them all".

These are a few of the measured responses to my article, a fortnight ago, about the film Loose Change, which maintains that the United States government destroyed the World Trade Centre and the Pentagon. Having spent years building up my leftwing credibility on behalf of my paymasters in MI5, I've blown it. I overplayed my hand, and have been exposed, like Bush and Cheney, by a bunch of kids with laptops. My handlers are furious.

I believe that George Bush is surrounded by some of the most scheming, devious, ruthless men to have found their way into government since the days of the Borgias. I believe that they were criminally negligent in failing to respond to intelligence about a potential attack by al-Qaida, and that they have sought to disguise their incompetence by classifying crucial documents.

I believe, too, that the Bush government seized the opportunity provided by the attacks to pursue a longstanding plan to invade Iraq and reshape the Middle East, knowing full well that Saddam Hussein had nothing to do with 9/11. Bush deliberately misled the American people about the links between 9/11 and Iraq and about Saddam Hussein's weapons of mass destruction. He is responsible for the murder of many tens of thousands of Iraqis.

But none of this is sufficient. To qualify as a true opponent of the Bush regime, you must also now believe that it is capable of magic. It could blast the Pentagon with a cruise missile while persuading hundreds of onlookers that they saw a plane. It could wire every floor of the twin towers with explosives without attracting attention and prime the charges (though planes had ploughed through the middle of the sequence) to drop each tower in a perfectly timed collapse. It could make Flight 93 disappear into thin air, and somehow ensure that the relatives of the passengers collaborated with the deception. It could recruit tens of thousands of conspirators to participate in these great crimes and induce them all to have kept their mouths shut, for ever.

In other words, you must believe that Bush, Cheney, Rumsfeld and their pals are all-knowing, all-seeing and all-powerful, despite the fact that they were incapable of faking either weapons of mass destruction or any evidence at Ground Zero that Saddam Hussein was responsible. You must believe that the impression of cackhandedness and incompetence they have managed to project since taking office is a front. Otherwise you are a traitor and a spy.

Why do I bother with these morons? Because they are destroying the movements some of us have spent a long time trying to build. Those of us who believe that the crucial global issues - climate change, the Iraq war, nuclear proliferation, inequality - are insufficiently debated in parliament or congress, that corporate power stands too heavily on democracy, that war criminals, cheats and liars are not being held to account, have invested our efforts in movements outside the mainstream political process. These, we are now discovering, are peculiarly susceptible to this epidemic of gibberish.

The obvious corollorary to the belief that the Bush administration is all-powerful is that the rest of us are completely powerless. In fact it seems to me that the purpose of the "9/11 truth movement" is to be powerless. The omnipotence of the Bush regime is the coward's fantasy, an excuse for inaction used by those who don't have the stomach to engage in real political fights.

Let me give you an example. The column I wrote about Loose Change two weeks ago generated 777 posts on the Guardian Comment is Free website, which is almost a record. Most of them were furious. The response from a producer of the film, published last week, attracted 467. On the same day the Guardian published my article about a genuine, demonstrable conspiracy: a spy network feeding confidential information from an arms control campaign to Britain's biggest weapons manufacturer, BAE Systems. It drew 60 responses. The members of the 9/11 cult weren't interested. If they had been, they might have had to do something. The great virtue of a fake conspiracy is that it calls on you to do nothing.

The 9/11 conspiracy theories are a displacement activity. A displacement activity is something you do because you feel incapable of doing what you ought to do. A squirrel sees a larger squirrel stealing its horde of nuts. Instead of attacking its rival, it sinks its teeth into a tree and starts ripping it to pieces. Faced with the mountainous challenge of the real issues we must confront, the chickens in the "truth" movement focus instead on a fairytale, knowing that nothing they do or say will count, knowing that because the perpetrators don't exist, they can't fight back. They demonstrate their courage by repeatedly bayoneting a scarecrow.

Many of those who posted responses on Comment is Free contend that Loose Change (which was neatly demolished in the BBC's film The Conspiracy Files on Sunday night) is a poor representation of the conspiracists' case. They urge us instead to visit websites like 911truth.org, physics911.net and 911scholars.org, and to read articles by the theology professor David Ray Griffin and the physicist Steven E Jones.

Concerned that I might have missed something, I have now done all those things, and have come across exactly the same concatenation of ill-attested nonsense as I saw in Loose Change. In all these cases you will find wild supposition raised to the status of incontrovertible fact, rumour and confusion transformed into evidence, selective editing, the citation of fake experts, the dismissal of real ones. Doubtless I will now be told that these are not the true believers: I will need to dive into another vat of tripe to get to the heart of the conspiracy.

The 9/11 truthers remind me of nothing so much as the climate change deniers, cherry-picking their evidence, seizing any excuse for ignoring the arguments of their opponents. Witness the respondents to my Loose Change column who maintain that the magazine Popular Mechanics, which has ripped the demolition theories apart, is a government front. They know this because one of its editors, Benjamin Chertoff, is the brother/nephew/first cousin of the US homeland security secretary Michael Chertoff. (They are, as far as Benjamin can discover, unrelated, but what does he know?)

Like the millenarian fantasies which helped to destroy the Levellers as a political force in the mid-17th century, this crazy distraction presents a mortal danger to popular oppositional movements. If I were Bush or Blair, nothing would please me more than to see my opponents making idiots of themselves, while devoting their lives to chasing a phantom. But as a controlled asset of the new world order, I would say that, wouldn't I? It's all part of the plot.

Monbiot.com