It is common for a particular work to be described as pivotal in a playwright's career and development. But in the case of Bash: Latterday Plays, currently being revived at the Trafalgar Studios in London, it would be no exaggeration to say that it changed its author's life. It was Neil LaBute's first published play, though it is actually comprised of three short pieces: a duologue sandwiched between two monologues, each part updating a different Greek tragedy to modern-day America with the gruesomeness intact.

When it first appeared under the title Bash: a Remembrance of Hatred and Longing in the December 1995 issue of Sunstone, a forum for the discussion of Mormonism in a cultural context, LaBute was himself a member of the Church of Jesus Christ of Latter-Day Saints. On the phone from Calgary, Canada, where he is working on a television series, the 51-year-old playwright and filmmaker insists he had no inkling of the trouble he would cause by writing three pieces that could easily have been subtitled "Mormons Do the Nastiest Things".

"It wasn't until the first production was reviewed in 1999 and got national attention that I heard anything from the church," he says, sounding comically exasperated even after all this time. He had become a filmmaker by this point, with a pair of fastidiously savage dramas to his name: In the Company of Men, in which two men woo a hearing-impaired female colleague as part of a cruel and clinical experiment, and Your Friends and Neighbours, which multiplied the miserable or misanthropic characters, among them an emotionally sadistic doctor who recounts tenderly his memory of raping a male classmate at college.

"Those films had way more explicit material than Bash," he says. "You'd think that would have made the church sit up and take notice. The difference was that the characters in them weren't Mormons." Even once objections were voiced over Bash, which features Mormon characters recounting confessions of murder, hate crimes and infanticide, many of the church elders hadn't even seen the play. "They noticed the reviews. I'm not even sure they read them. But one in particular had the headline 'Murderous Mormons'. So, you know, it wasn't seen as good PR. Those two words don't look good together."

He was disfellowshipped, a step short of excommunication – it still permits a way back, a reprieve. But rather than forcing LaBute to change his writing, it led him to examine the limits of his own faith: "I had to make the decision to go forwards or backwards. I couldn't live in that limbo and decided it was better for me not to be a Mormon than to be a 'bad' Mormon. I don't think I was ever really devout enough. When someone would ask me if I was a practising Mormon, I would reply flippantly, 'Yes, but I need more practice.' I was doing things blatantly that Mormons were not supposed to do. Members of the church are asked not to see R-rated movies and here I was making R-rated movies – spending most of my days crafting them. At some point you hold up these two different ideas of yourself and choose between them."

It might be assumed that subsequent changes LaBute made to the text of Bash, removing the references to the characters' religion, were intended to mollify the church, but this wasn't the case, he claims. Each of his plays is a live text, subject to revisions and updates – he wrote an extra scene for Some Girl(s) which appeared in the published version, and has written new material for a revival of Fat Pig that he hopes to stage on Broadway. (He is also considering rewriting his 2001 play The Shape of Things to take into account modern phenomena such as social media.)

In modifying Bash, LaBute was responding to a growing realisation that the play's religious context had let some audiences off the hook. "It allowed those who were not Mormons to detach themselves from it a little bit: 'Oh, that couldn't be me because I'm not a Mormon.' Or it led people to think: 'Ah, so apparently Mormons are like Nazis, and you'd better not piss them off else they'll kill you.' That was never the idea. I thought I should do a version that made it more general because we could all be these people. We all have the capacity to do bad."

It's characteristic of LaBute to tailor his work so it agitates or unsettles the largest possible range of people; he admits to dedicating himself to subverting the balance of power in theatre, where the audience has the upper hand. "I'm always looking for ways to bring that experimentation into my work," he explains.

A key example was his own Almeida production of The Shape of Things, about a woman (Rachel Weisz) who manipulates her boyfriend (Paul Rudd) into changing everything about his life and his appearance in what transpires to be – you guessed it – another cruel and clinical experiment: "I played the music really loud between scenes so that people were holding their ears. We actually brought in a sound technician to see how loud we could play it and still be within health and safety rules. I didn't want people being able to talk to one another between scenes."

More controversial was his decision to do away with curtain calls on that show. "I didn't want to wrap it up with that false moment where the actors come back on and say, 'Everything's okay!' After the play had been reviewed, I implemented a system where the stage manager could roll a dice to decide which of the actors would get a curtain call, so it would change every night. Curtain calls are a way for the audience to make eye contact, to say: 'We can be friends.' Occasionally I want to say: 'I don't wanna be friends! This is not a friendly thing. This is a contest to see who can push each other around the hardest.'"

More on Neil LaBute

• Portrait of the artist: Neil LaBute

• Quiz: Do you speak LaBute?