Earlier this year, when critics raised questions about the historical accuracy of Morten Tyldum's film The Imitation Game, in which Benedict Cumberbatch plays the Enigma codebreaker Alan Turing, the writer of its screenplay, Graham Moore, accused them of "fact-checking art" – obviously a bad thing to do. "You don't," he added, "fact-check Monet's Water Lilies. That's not what water lilies look like. That's what the sensation of experiencing water lilies feels like." Faced with criticisms about the accuracy of Selma, her film about Martin Luther King, Ava DuVernay was similarly dismissive: "Everyone sees history through their own lens," she said. "And that should be valid."

It’s a perennial question, of course. Film-makers can’t resist the temptation to have it both ways with history: to present their stories both as true and as their own particular truth, shaped for emotional ends. To use Moore’s analogy, they tend to suggest to audiences that these are actual water lilies and to critics that only a fool would think they were real flowers.

Does this really matter? Do people come to believe untrue things that they have seen in movies? A question that occurred to me is whether there is any provable case of a “fact” invented or promulgated by the movies coming to be accepted by most people as truth. And I can think of at least one, a very potent political “truth” that has become part of the collective memory of the US and that influences big things like foreign policy and presidential elections.

One of the things that most people in the US and elsewhere "know" about the Vietnam War is that soldiers who served in that bitterly divisive conflict were spat at by protesters when they were getting off planes in San Francisco. The "spitting image", as Jerry Lembcke cleverly calls it in his book of the same name, dramatises a way of seeing one of the most important episodes in recent US history. Especially for conservatives, it encapsulates a stab-in-the-back theory of why the US lost that war: hippies and lefties turned on the brave boys who had done their duty and placed themselves in harm's way. Vets being spat on is a constant point of reference, not just in relation to Vietnam but also, in relation to more recent wars, as proof of the perfidy of anti-war protests in general.

But the spitting never happened. In an era already saturated with cameras, there is not a single contemporary photograph of a protester spitting at a returning soldier. Nor is there a single contemporary news report of spitting either being witnessed by a reporter or complained of by a soldier. In 1995 three sociologists at the University of California studied 495 reports from the New York Times, Los Angeles Times and San Francisco Chronicle of anti-war protests that contained "any portrayal that implied, even indirectly, a troop-blaming orientation". Not one mentioned spitting. Nor is there any mention in any known surveillance file – protests were closely observed by the FBI – of spitting.

In fact the only contemporary mention of spitting at an anti-war protest does not refer to anti-war protesters spitting at soldiers. Ironically, it refers to a threat by pro-war counterdemonstrators to spit at a man named Dave Moss, who was reading out the names of dead soldiers in public. Life magazine reported the incident in Texas in 1969, with the pro-war demonstrators shouting, "Spit at those people, spit on 'em," "Hippies!" and "Dirty commies!"

There’s a very good reason why the spitting on returning vets didn’t happen: the great strength of the anti-Vietnam War movement was that it was partly led by vets themselves. The thrust of the protest movement was immensely sympathetic to the conscripts, whom it saw as victims of the war policy and who were, in turn, increasingly politicised. It was partly the threat of large-scale mutiny by vets that forced the US to pull out of Vietnam. The “spitting image” is a way of painting out of history the extraordinary alliance between veterans and the anti-war movement.

But how did the image take hold? Almost certainly through the figure of Sylvester Stallone's enraged vet in Rambo: First Blood. He wails, about being in Vietnam, "I did what I had to do to win. But somebody wouldn't let us win. Then I come back to the world and I see all those maggots at the airport. Protesting me. Spitting. Calling me baby killer and all kinds of vile crap."

Whether or not Rambo's image feeds on a myth that was already circulating, it made it a "fact". And that fact became so potent that by the time John Kerry, a leader of the veterans' anti-war movement, was running for president, veterans were "remembering" being spat at at the airport. The image satisfied a deep need to explain why the US lost the war: somebody wouldn't let us win, and that somebody was vile enough to engage in the repulsive act of spitting.

Here is at least one instance in which we can see that “fact-checking” art may not be such a bad idea sometimes. It is true, as DuVernay claimed, that everyone sees history through his or her own lens, but some lenses distort more than others. And in the end what is seen through them is not history but propaganda.

fotoole@irishtimes.com