When I returned from the war in Vietnam, I wrote a film script as an antidote to the myth that the war had been an ill-fated noble cause. The producer David Puttnam took the draft to Hollywood and offered it to the major studios, whose responses were favourable - well, almost. Each issued a report card in which the final category, "politics", included comments such as: "This is real, but are the American people ready for it? Maybe they'll never be."

By the late 1970s, Hollywood judged Americans ready for a different kind of Vietnam movie. The first was The Deer Hunter, which, according to Time, "articulates the new patriotism". The film celebrated immigrant America, with Robert De Niro as a working-class hero ("liberal by instinct") and the Vietnamese as subhuman oriental barbarians and idiots, or "gooks". The dramatic peak was reached during recurring orgiastic scenes in which GIs were forced to play Russian roulette by their Vietnamese captors. This was made up by the director, Michael Cimino, who also made up a story that he had seen military service in Vietnam. "I have this insane feeling that I was there," he said. "Somehow . . . the line between reality and fiction has become blurred."

Ecstatic critics treated The Deer Hunter as virtually a documentary. "The film that could purge a nation's guilt!" said the Daily Mail. President Carter was moved by its "genuine American message". Catharsis was at hand. Vietnam movies became a revisionist popular history of the great crime in Indochina. That more than four million people had died terribly and unnecessarily, and that their homeland had been poisoned to a wasteland, was not the concern of these films. Rather, Vietnam was an "American tragedy", in which the invader was to be pitied in a blend of false bravado and angst: sometimes crude (the Rambo films) and sometimes subtle (Oliver Stone's Platoon). What mattered was the strength of the purgative.

None of this, of course, was new: it was how Hollywood created the myth of the Wild West, which was harmless enough unless you happened to be a Native American; and how the Second World War has been relentlessly glorified, which may be harmless enough unless you happen to be one of countless innocent human beings, from Serbia to Iraq, whose deaths or dispossession are justified by moralising references to 1939-45. Hollywood's gooks, its Untermenschen, are essential to this crusade - the despatched Somalis in Ridley Scott's Black Hawk Down and the sinister Arabs in movies such as Rendition, in which the torturing CIA is absolved by Jake Gyllenhaal's good egg.

Emitting safe snipes and sneers, film critics promote a deeply political system that dominates what we pay to see

As Robbie Graham and Matthew Alford pointed out in the New Statesman (2 February), in 167 minutes of Steven Spielberg's Munich, the Palestinian cause is restricted to just two and a half minutes. "Far from being an 'even-handed cry for peace', as one critic claimed," they wrote, "Munich is more easily interpreted as a corporate-backed endorsement of Israeli policy."

With honourable exceptions, film critics rarely question this, or identify the true power behind the screen. Obsessed with celebrity actors and vacuous narratives, they are the cinema's lobby correspondents. Emitting safe snipes and sneers, they promote a deeply political system that dominates most of what we pay to see, knowing not what we are denied. Brian De Palma's 2007 film Redacted shows an Iraq the media do not report. He depicts the homicides and gang rapes that are never prosecuted and are the essence of any colonial conquest. In the New York Village Voice, the critic Anthony Kaufman, in abusing the "divisive" De Palma for his "perverse tales of voyeurism and violence", did his best to taint the film as a kind of heresy and to bury it.

In this way, the "war on terror" - the conquest and subversion of resource-rich regions of the world, whose ramifications and oppressions touch all our lives - is virtually excluded from the popular cinema. Michael Moore's outstanding Fahrenheit 9/11 was a freak; the notoriety of its distribution ban by the Walt Disney Company helped it to force its way into cinemas. My own 2007 film The War on Democracy, which inverted the "war on terror" in Latin America, was distributed in Britain, Australia and other countries but not in the United States. "You will need to make structural and political changes," said a major New York distributor. "Maybe get a star like Sean Penn to host it - he likes liberal causes - and tame those anti-Bush sequences."

During the Cold War, Hollywood's state propaganda was unabashed. The classic 1957 dance movie Silk Stockings was an anti-Soviet diatribe interrupted by the fabulous footwork of Cyd Charisse and Fred Astaire. These days, there are two types of censorship. The first is censorship by introspective dross. Betraying its long tradition of producing gems, escapist Hollywood is consumed by the corporate formula: just make 'em long and asinine and hope the hype will pay off. Real talent is absorbed. Ricky Gervais is his clever comic self in Ghost Town, while around him stale, formulaic characters sentimentalise the humour to death.

These are extraordinary times. Vicious colonial wars and political, economic and environmental corruption cry out for a place on the big screen. Yet try to name one recent film that has dealt with these, honestly and powerfully, let alone satirically. Censorship by omission is virulent. We need another Wall Street, another Last Hurrah, another Dr Strangelove. The partisans who tunnel out of their prison in Gaza, bringing in food, clothes and medicines, and weapons with which to defend themselves, are no less heroic than the celluloid-honoured POWs and partisans of the 1940s. They and the rest of us deserve the respect of the greatest popular medium.