The San Francisco Gay Men’s Chorus has always been profoundly political. Founded in 1978, the 300-strong group, widely regarded as launching the gay choral movement, had its first public performance at city hall after the assassinations of Mayor George Moscone and supervisor Harvey Milk.

After four decades of concerts, social acceptance of LGBTQ people grew, but the 2016 presidential election left its leadership and members reeling. Singing for Our Lives was the song they performed after the death of America’s first openly gay public official, and its lyrics seemed alarmingly pertinent once again, so the chorus teamed up with the Oakland Interfaith Gospel Choir on a 2017 Lavender Pen tour through the region that had embraced Trumpism most fully.

David Charles Rodrigues’s documentary Gay Chorus Deep South follows the two groups through states such as Mississippi, Tennessee and North Carolina. A redemptive tale that bridges cultural divides in the wake of the 2016 election, the film follows several narrative arcs to establish that misunderstandings existed on both sides.

To its credit, Gay Chorus Deep South doesn’t recycle tired tropes from George W Bush-era cultural liberalism. This is a project in search of rapprochement, from winning over homophobic hearts one by one to marching over the Edmund Pettus Bridge in Selma, Alabama, in a gesture of intersectional solidarity.

Anchoring the film is Tim Seelig, SFGMC’s director, who has his own history with the south. An active Southern Baptist and megachurch chorus director in Houston, he eventually came out as a gay man in his 30s. The denomination’s hierarchy took swift action, and he quickly lost his family and job, later relocating to Dallas. Even decades later, Seelig admits: “I hate the church for the things they did to my family.” Gay Chorus Deep South quietly insists that social progress requires individual action as well as structural change, and the film is in no small part Seelig’s attempt at both. He eventually reconciled with both his son and daughter, he said, but only after his son changed his name to avoid any association with his father, by then a well-known figure in Dallas.

“I would say ‘estranged’ is a mild word for what we were for seven or eight years,” Seelig says, adding that it was his son’s future wife who urged the reconnection. “He’s living his life and he’s a wonderful man and a wonderful father. I think he’s fantastic.”

While this resolution isn’t depicted in the film itself, sweet moments abound. During one performance, a chorus member’s staunchly antigay father can’t help but smile at a drag queen singing Patsy Cline’s She’s Got You and pulling various relationship mementoes out of her cleavage – then a flask, then a handsaw. A straight-up gooey, tender moment involves a childhood friend of a chorus member giving him a quilt she’d sewn. Her politics are implied to be to the right of his, but she uses the idea of a quilt as a metaphor for strength in unity.

For director Rodrigues, a particularly emotional speech the otherwise unflappable Seelig delivers at one performance was “a cathartic moment for Tim and for me”.

“I was so entrenched with him that I felt all the emotions that were going through him,” Rodrigues says, adding that he also started to cry: “I was afraid I was going to short-circuit the monitor.”

Gay Chorus Deep South is full of It Gets Better-esque encouragement, especially as many of the venues were chosen because they are in states with brazenly anti-LGBTQ laws, Mississippi and North Carolina in particular. “You have to be who you needed when you were 14,” one chorus member says.

The catalyst for all this, it turns out, is the Oakland Interfaith Gospel Choir. A smaller and not particularly religious institution whose membership is approximately one-third LGBTQ-identified, the choir joined SFGMC on many of its dates, and its inclusion was vital.

“In the south, you don’t make change except through the church,” the chair of the SFGMC says in the film.

Throughout the tour, fans record testimonials attesting to the power of music to overcome injustice. At several stops, the combined ensembles meet with organizations such as the American Civil Liberties Union and student groups at various colleges.

Narrative tension remains constant throughout, between winning over individual hearts and minds and bringing about structural change, between the need to entertain and be hospitable versus the insufficiency of mere tolerance. It all leads up to a concert at a Southern Baptist church – Seelig’s first time inside one in decades. The performance is meant to “sprinkle water on some pretty dry land”, as he puts it, which could refer to his own religious roots or to states where it’s perfectly legal to fire someone for being a lesbian.

From a production standpoint, the operation was smoothly oiled from the start. But not everyone in the 300-member group relished the idea of performing in a region that had voted overwhelmingly for Donald Trump. No one refused outright, Seelig says, but several people feared for their personal safety.

Ashlé Blow, an African American member who came out as trans, was particularly apprehensive.

“We were all terrified it was going to be this dangerous situation, and on some level we were disappointed because we came emotionally armed and prepared to fight back or whatever, and there wasn’t any of that,” Blow says. “It taught us a lesson to not make assumptions, because we were doing the same thing that we feel the south does to us.”

In one scene, Blow and another chorister eat with a family so devout that they eschew musical instruments during worship, because they aren’t found in the New Testament. It was a five-hour meal, and people speak haltingly, hoping to find common ground that goes beyond icy tolerance.

There are, of course, unpleasant moments of open hatred, as when the chorus’s leadership stands around listening to a voicemail calling them “Gomorrah-ites” and “a bunch of perverts”. And protesters, some of them so called ex-gays, show up from time to time. But occasions when Seelig was all but spoiling for a fight, as with an appearance on an alt-right radio station in Knoxville, Tennessee, turn into surprise love-fests. Still, at least two churches reject outright the idea of a performance.

In spite of its increasingly cosmopolitan cities, the American south retains its reputation for discrimination rooted in religiosity. This makes the region either an unlikely or ideal spot for a showdown over what have long been known as “San Francisco values”. And Gay Chorus Deep South doesn’t shy away from interrogating the chorus’s own assumptions, either.

In a particularly tense scene, Josh Burford, a historian who works on LGBTQ experiences in the American south, calls the idea of a prominent national organization doing a goodwill tour “white paternalist and condescending”. Indeed, some of the young people the chorus members push back against the idea that if “you’re queer and in the south, you’re not OK”. But the film’s strength lies in articulating the need to move beyond mere civility, that spongy virtue that can permit injustice to continue by prioritizing the need to superficially get along. In a place where acceptance is far from universal, it seeks to make the LGBTQ community part of the community.

• Gay Chorus Deep South concludes its national tour with screenings in San Francisco from 22 to 24 November. MTV Films plans to release it on a streaming service soon.