In his time gazing into some of the United States' weirdest subcultures - from porn stars to UFO chasers - documentary filmmaker Louis Theroux was always in danger of "falling in".
"There's this sort of gravitational pull towards starting to identify with the contributors," he says, "a risk of slightly 'going native' that creates an interesting emotional dynamic in the shows."
But with the Scientologists it was different. Rather than become a convert, it was a battle not to feel repulsed by them.
My Scientology Movie comes after Theroux spent three years steeped in what is arguably one of the world's most shadowy and cult-like religions.
When the church caught wind of the project, its henchmen appeared like hornets from a nest - tailing him on the road, turning up unannounced during filming, and even making a documentary of their own - with him as the subject.
"The real risk was to start to see them as the enemy," he says. "I was striving very much to understand it in an empathetic way, so I had to resist it becoming a kind of 'us and them' paradigm, because I think a lot of Scientology coverage does fall into that trap."
He'd been fascinated with Scientology since the late '80s, and as he rose to fame with his Weird Weekends TV series, it remained in the back of his mind as potential fodder.
The church never opened its doors to him, so he took an approach that didn't depend on access.
"Although I was immersed in the concept, and I was immersed among ex-Scientologists, the only encounters I was having with actual paid-up Scientologists was when they were hassling me and hassling the people I was speaking to, by filming or shouting abuse at us."
The journalist set out to cast and shoot a movie depicting the most disturbing revelations from former members, using Hollywood actors and the guidance of prominent ex-Scientologist Marty Rathbun - and to document that process.
The resulting 'film within a film' (potentially within another film, if Scientology's own cinematic effort ever sees the light of day), is his first feature, produced by Oscar-winner Simon Chinn (Man on a Wire, Searching for Sugar Man).
Theroux's fans are accustomed to being steered on an even keel through the strange and uncomfortable, but there is a disturbing pitch to his confrontations with church members.
It feels something like first contact as the two parties collide, each with cameras trained on the other.
"One of the fascinating things about Scientology is that they fight back. It's not like other churches - you know Christianity, you think of turning the other cheek - well that idea doesn't exist in Scientology, as far as I know.
"In fact, they believe that if you're under attack as a Scientologist, you have a license to destroy that person."
At one point the church's ongoing harassment of Rathbun sent him over the edge; he lost his temper at Theroux and the whole project threatened to derail.
Rathbun, who he describes as the "heart and soul" of the film, was the right-hand man to the head of Scientology, David Misgavich, for many years, and involved in the "dark arts" of keeping the religion going when he was inside it.
Theroux says he enjoyed Rathbun's company and found his spikiness appealing, although director John Dower tended to have a "smoother" relationship with their unpredictable guide.
"When someone's shouting at you, obviously it's a little bit uncomfortable. It's not something I welcome. But clearly there's a moment in the film when I ask a question that's rather pointed and possibly ill-judged in terms of when I asked it… and [Rathbun] reacted quite badly and sort of abused me. But you know, maybe I deserved that, to be honest with you."
He faces a tricky balancing act with all of his documentary subjects - often growing emotionally attached to them, and vice versa.
"It's an odd relationship that you have with someone who is both the subject of what you're doing, and also someone who you feel you are growing to like."
In his career to date, he's been most enchanted by worlds in which he was made to feel welcome, or there appeared to be a certain amount of goodwill. One of them was a brothel in the desert.
"It may sound a bit odd but in the three weeks I spent filming at a brothel in Nevada, I began feeling somehow at home there - and I don't mean because it was in any way sexually beguiling - I just mean that there was a sense of it being almost like a refuge.
"There was a lot of warmth and humanity in the way that people interrelated – there was a surprising amount of tenderness."
He experienced that same sense of unlikely kinship during the making of The Most Hated Family in America, about the family at the core of the Westboro Baptist Church. The fanatical Christian group is notorious for protesting at the funerals of US soldiers with signs that display text such as "God Hates Fags".
"Even at Westboro Baptist Church, though I never felt the beliefs were anything other than hateful, I spent enough time there to see how... by projecting so much hate outwards, they were buttressing themselves and creating a closeness among themselves."
He does not set out to upset people with his projects - not even Scientologists. The people who have been left unhappy with his treatment of them are in a minority, and when it does happen, "you just have to take it on the chin".
"The bottom line is you do what you feel is a reasonable job, a fair job - clearly it would be nice if people all liked the documentaries that they appeared in."
The late Jimmy Savile - a British TV personality exposed as a serial paedophile after his death - was unexpectedly approving of Theroux's film When Louis Met Savile, an unsettling look into his eccentric life. In the film, Louis raises the rumours of paedophilia which exploded after Savile's death, and which Savile denied.
Despite being endlessly difficult during filming, Savile said he was pleased with the finished product, and Theroux kept in touch with him.
"He was someone who didn't like to ever be seen as being weak, or to be perceived as having someone get the better of him," he recalls.
"Even if he hadn't liked [the film], or he'd been worried about it, he wouldn't have let on. But he did say that he liked it."
Understandably now regretting his odd friendship with Savile, and perhaps feeling guilty for not pressing him further on his rumoured paedophilia, Theroux has just released a film reflecting on the one he made 16 years ago; in Louis Theroux: Savile, he speaks to the predator's victims and former employees, and asks them what they thought of his original piece.
It's the latest instalment in the 46-year-old's general departure from cultural fringes to more pressing social issues, including alcoholism and mental illness. He won't be drawn on what he's working on next, although he does drop a hint: "I'm back in America."
He would like to make another feature film, but for now, his Hollywood adventure is at an end. The Scientologists appear to have left him alone, and it's "back to the grind of TV".
"It was a wonderful experience doing the movie; a different team around me, more resources, a bigger sense of ambition, and to be telling a story that for years I thought I would never be able to tell," he says.
"To finally sort of put all the hours I'd spent over the years thinking about it, reading up on it, looking at stuff on the internet - to finally put that to use was like a massive purging."
My Scientology Movie is released in select New Zealand cinemas by Madman Entertainment on October 13.