Last December, when the movie Brokeback Mountain nudged nervously onto the cultural radar screen in the US, the consensus was broad and wide. This movie was one step too far. It was yet another example of Hollywood’s liberal bias. It wouldn’t sell in the heartland.

“They’re not going to go see the gay cowboys in Montana. I’m sorry. They’re not going to do it,” opined cable television’s chief windbag Bill O’Reilly on December 20.

The liberal blogger Mickey Kaus wrote around the same time: “I’m highly sceptical that a movie about gay cowhands, however good, will find a large mainstream audience. I’ll go see it, but I don’t want to go see it . . . When the film’s national box office fails to live up to its hype and to the record attendance at a few early screenings, prepare to be subjected to a tedious round of guilt-tripping and chin- scratching.”

The Washington Post columnist Charles Krauthammer made a new year’s prediction about Oscar night: “Brokeback Mountain will have been seen in the theatres by 18 people — but the right 18 — and will win the Academy Award.”

Something odd happened between the elite’s assessment of the heartland and the heartland’s assessment of Brokeback Mountain. No, it’s no The Lion, Witch and the Wardrobe. But of all the Oscar nominees it has racked up by far the biggest domestic grosses so far: more than $70m at the last count (compared with, say, $22m for the superb Capote). And that’s before the potential Oscar boost. More interestingly, it’s done remarkably well in the middle of the red states.

O’Reilly’s Montana? In the 85-year-old cinema in Missoula, Montana, the owner told the media: “It’s been super every night since we started showing it.” The movie did even better in Billings, a more conservative city in the state.

According to Variety magazine, some of the strongest audiences have been in Tulsa, Oklahoma, El Paso, Texas, Des Moines, Iowa and Lubbock, Texas. Lubbock is the place George W Bush calls his spiritual home and may well be the site for his presidential library. Greenwich Village it ain’t.

What happened? There are various theories. Brilliant marketing pitched the movie as a love story and a western, two genres well ingrained in middle American tastes. Women dragged nervous husbands and boyfriends to see a film where the women could enjoy long, languorous views of Heath Ledger and Jake Gyllenhaal, and the men could admire the scenery.

Blue state liberals felt it some kind of social duty to see the film. Gays and lesbians flocked. The media hyped the “gay cowboy” movie and it generated more and more publicity, and thereby curiosity and thereby tickets.

The iconic phrase uttered by Gyllenhaal — “I wish I knew how to quit you” — has become part of the popular culture. The cover of last week’s New Yorker had a parody of the now-famous poster, with Bush and Dick Cheney as the cowboys and Cheney blowing some steam off the top of his rifle.

Everyone seems to have an opinion about the film, especially those who haven’t seen it. My own view is that Brokeback has done well primarily because it’s an excellent film. It has a compelling story, two astonishing performances from Ledger and Michelle Williams, and an elegant screenplay from the great western writer Larry McMurtry.

I still don’t think the movie is in the same class as the brilliantly compressed short story by Annie Proulx on which it’s based. But it’s still way better than most films now offered by Hollywood, and it’s a little depressing that we have to ask why a decent number of people would not want to see a rare example of Hollywood excellence.

As for the gay sex, it’s barely in the movie, and the least convincing part of it. Compared with the sex and violence usually served up by Hollywood films, Brokeback is Jackanory. But there is something, perhaps, that explains the interest beyond mere artistic skill.

The past two decades have seen a huge shift in how homosexual people are viewed in the West. Where once they were identified entirely by sex, now more and more recognise that the central homosexual experience is the central heterosexual experience: love — maddening, humiliating, sustaining love.

That’s what the marriage debate has meant and why the marriage movement, even where it has failed to achieve its immediate goals, has already achieved its long-term ambition: to humanise gay people, to tell the full, human truth about them.

And that truth includes the red states. The one thing you can say about the homosexual minority is that, unlike any other, it is not geographically limited and never has been. Red states produce as many gay kids as blue ones; and yet the heartland gay experience has rarely been portrayed and explored.

In America this is particularly odd, since the greatest gay writer in its history, Walt Whitman, was a man of the heartland. And you only have to read about the early years of Abraham Lincoln’s life to see that same-sex love and friendship was integral to the making of America, especially in its wildernesses and frontiers. You see that today even in the American gay vote, a third of which routinely backs Republicans.

Brokeback, in other words, is not just a good movie, but a genuinely new one that tells a genuinely old story. It shows how gay men in America have families and have always had families. It shows them among themselves and among women. It shows them, above all, as men.

For the first time it reveals that homosexuality and masculinity are not necessarily in conflict, and that masculinity, even the suppressed, inarticulate masculinity of the American frontier, is not incompatible with love.

It provides a story to help people better understand the turbulent social change around them and the history they never previously recorded. That is what great art always does: it reveals the truth we are too scared to see and the future we already, beneath all our denial, understand.

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