It all seems too quaint now: the “boycott,” the death threats, the CD-trashing parties, enraged protesters at fluffy pop concerts

The idea that there were performers who had the temerity to question America’s rush to invade Iraq in 2003, to mock America’s now increasingly mocked chief executive pushing for it – and the price they paid – feels like ancient history.

But here they are, bluegrass-pop stars the Dixie Chicks, re-living their firestorm of controversy in “Shut Up & Sing.” This lively, eye-opening documentary from veteran lefty and music filmmaker Barbara Kopple (“Harlan County, USA”) captures the Chicks as Natalie Maines makes her infamous off-hand crack about being “ashamed” that President George W. Bush is from Texas while onstage in Britain. We see their obliviousness to the reaction back home, their failed efforts at damage control.

And we see them ride out the years of fallout and blow-back, arriving, finally, at something resembling exoneration, 3,000 dead Americans later.

Kopple (and co-director Cecilia Peck) juxtapose the beginning of the end for the Chicks – (Maines, Emily Robison and Martie Maguire), then country music’s top-selling act, their “Top of the World” tour – against Bush’s high-water mark, his now infamous flight-suited arrival on an aircraft carrier beneath the banner “Mission: Accomplished.”

The film follows the Chicks through 2003, with their backs up (outspoken Maines, in particular, is unrepentant) and conservative country-music radio and conservative Web sites mounting a boycott against them. The movie picks them up again in 2005 and now 2006, in the studio to cut a defiant album, trying to sell Taking the Long Way without the nation’s big-radio empires – Cox, Cumulus and others refuse to play their music.

Their British manager miscalculates even as he bends over backward to allow them to express themselves freely and keep their integrity. Their poor publicist sees an Entertainment Weekly cover of the ladies, nude, painted in the labels their critics were hurling at them (“unpatriotic”), as a bad move merely fanning the flames.

We see the group rally around Maines and eventually accept that their bread and butter – country music – has abandoned them.

Maines’ hometown (Lubbock, Texas) country-music DJ hits on it when he says they stuck their finger in the eye of the people they make their living from.

The movie’s best moments are those scenes that capture the Chicks not realizing what they’ve done, trying not to criticize Maines (the singer who brought them to the top) and then circling the wagons against the ugliness hurled at them. In today’s polarized America, you pick who you stand with, even in pop culture. Kopple’s film makes that choice stark – the talented and the beautiful, versus drawling, pot-bellied haters, waving signs outside their concerts.

Documentaries lose their objectivity in the editing, and I’m betting that Kopple and Peck had more footage of the other chicks questioning Maines and what she has cost them. If not, they were hiding their feelings. But the end result, that they were brought together, made stronger if a bit more self-righteous by the process, is undeniable. Their audience is smaller, but it is made up of true believers, now.

And the movie, with its pregnant, dolled-up and somewhat coarse singers caught off the cuff, and its many images of the cranks and rubes allied against them, won’t do the Dixie Chicks any favors.

Because in showbiz and politics, it’s not enough to be “right.” It’s hard to make money off folks who don’t like being reminded they were wrong.