Few British bands are so polarising as Bristol indie-punks Idles. To some (particularly those who spend a lot of time online), their declarative songs about love, Tories, racism and other big topics are glib, even damaging in their blunt sloganeering. To others, they are vitally important broadsides against a hateful world.

This documentary by Mark Archer very much panders towards the latter category, as it follows the band from their inception in 2009 to their triumphant, tearful Glastonbury performance in 2019. But it makes a virtue of it, with some of its most emotive footage coming from interviews with members of the band’s AF Gang online fanclub and their “this band saved my life” testimonies.

The editing, of enjoyably intimate footage from backstage, on stage, under stagedives and back in the tour bus, keeps the tempo as high as their hits. There are some droll juxtapositions of rather fastidious frontman Joe Talbot, fretting about tidiness, with the definitively louche guitarist Mark Bowen doing his interviews in a hot tub. Footage of touring in the US mists romance into the final act, but by the end it starts to feel like indulging a neighbour’s holiday slideshow. Even weaker are Steve Lamacq and the Maccabees’ Felix White with some deeply tame anecdotes about the band that you had to be there for, though you’re really not bothered you weren’t.

But Archer does a good job of showing first the Bristol that they emerged from rather against the odds – described fondly as the “arsehole of ambition” by bassist Adam Devonshire – and then the trauma that helped catalyse the band’s anger and humanism: the deaths of Talbot and Devonshire’s mothers in quick succession, and then the stillbirth of Talbot’s first child. Idles are a very sentimental band in their way, explaining why they are both loved and despised, but discussion of these trials is filmed unsentimentally, with Talbot frank and emotionally intelligent: “I’m learning to love myself by talking about the things that are broken in me.”

This anti-ironising stance was always going to take a battering in the whirl of bad faith online, though not always without merit. Talbot is filmed earnestly telling an American audience “forget the racists, they don’t exist for now, let’s celebrate each other”, which deserves an eye-roll. What is sometimes forgotten is that Idles are a punk band, and slogans suit them: in a world of fiendish micro-aggressions, it’s bracing to have obvious stuff said in a simple way. Archer doesn’t press Talbot to elaborate on statements such as “our band is shaped around not compromising the art for bullshit” … What bullshit? Well, perhaps it’s for their fans to apply these multi-purpose bromides to their own lives, and it’s that generosity of spirit that those fans have latched on to. This film is for them, and its earnest, puppyish energy is apt.

• Don’t Go Gentle: A Film About Idles is released on 2 July in cinemas.