No documentary has inspired more controversy at this year’s Sundance Film Festival than “Going Clear: Scientology and the Prison of Belief.”

It’s a devastating portrait of a religion guided by greed, instead of motivated by altruism. The film alleges that Scientology abuses its rank and file, hitting them up constantly for money, while, in some cases, subjecting them to physical and psychological degradation.

It also points the finger of blame squarely at two of Scientology’s most famous practitioners, John Travolta and Tom Cruise, and shames them for turning a blind eye to the alleged mistreatments.

It’s another hot-button topic for documentary filmmaker Alex Gibney, who took on Wikileaks and Enron in previous films such as “The Smartest Guys in the Room” and “We Steal Secrets.”

Variety sat down with Gibney and Lawrence Wright, the Pulitzer Prize-winning journalist who wrote the book that formed the basis for the film, to discuss Scientology’s links to Hollywood, its alleged abuse of its tax-exempt status and why Cruise and other stars are vital to its survival.

Why has Tom Cruise become the symbol of this religion and how important is he to the church?

Alex Gibney: He’s vital to the church, because he is the most famous Scientologist.

He is their key guy and he is a magnet for people. Very often you’ll ask people what’s Scientology and they’ll say, ‘isn’t that the religion with Tom Cruise’? So he’s their poster boy.

Why is Scientology so entwined with the entertainment business?

Lawrence Wright: This goes back to the founding; when L. Ron Hubbard created the Church of Scientology, he decided to make its headquarters in Hollywood, because he had a very perceptive notion that there is something that all Americans do worship and it’s celebrity and the capital of celebrity is Hollywood. He set out very early to make it a Scientology town.

They always wanted celebrities who could sell Scientology just like the people on the front of the Wheaties box.

Both the book and film are critical of celebrities like Tom Cruise and John Travolta. What culpability do they have in some of the abuses that you allege the church is guilty of?

AG: By now there is a well-documented record of abuses in the Church of Scientology, yet Cruise and Travolta have never spoken out about them. By not speaking out, it’s a kind of an endorsement and I think that’s why we’re right and properly critical.

LW: They’re selling a product and the product they’re selling is oppressing some of the people inside the church, especially the clergy, which is called the Sea Org, and Cruise has spent countless hours out on the Sea Org base where — on that same base where he has a special chateau — there’s these double wide trailers called the hole, which is a kind of re-education camp where people have been incarcerated for years. Sleeping on the floor on bedrolls with ants crawling around, abused physically, made to lick the floor or the toilet with their tongue. It’s just unbelievable degradation.

If he’s ignorant of that, then it’s willful on his part.

AG: The other thing about Cruise is that he’s been the beneficiary of this unbelievably low-paid Sea Org labor. These people are being paid forty cents an hour and they’re tricking out Cruise’s cars.

LW: We hold people like Tom Cruise and John Travolta and others responsible for not demanding change inside that church.

What’s been the impact of screenwriter and director Paul Haggis’ decision to quit the church and the note he released criticizing the organization?

LW: Paul was really the vanguard. There were a lot of celebrities that had been in the church and left quietly and never really wanted to make their membership known. Paul was the first to leave loudly. He was angry.

His example has, I think, inspired many other Scientologists to look closely at the religion. And actually what is so remarkable about Paul’s story is that for 35 years he didn’t look. This is a typical story where you’re told not to look on the internet. Don’t look at anything disparaging, so he never heard a bad word about Scientology for 34 of those 35 years.

The church has released a statement saying that you did not seek out their members for interviews and you did not give it an opportunity for comment. What’s your reaction?

AG: We reached out for interviews with the people that were relevant to our story. Scientology wanted to send us a delegation of 25 unidentified individuals, presumably to smear the people in our film. I wasn’t interested in that.

Do films and books like “Going Clear” feed a persecution complex on the part of Scientologists? Do they strengthen their bond to their faith?

AW: Probably it feeds a kind of persecution complex at the very top. One thing I’ve discovered over time, having done a number of films about abuses of power, is very often the most powerful people are the ones who feel the most victimized, particularly by criticism.

The testimony of a lot of these people like Paul and others who have left is actually giving tremendous comfort to many people who have been roundly abused and ultimately need the courage to leave the church, because one of the hardest things in leaving the church is to be able to recognize that you’ve made such a terrible mistake for so long.

When people do speak out, what dangers do they face?

AG: Very often they’re smeared. Very often people they work with get letters denigrating them, sometimes trying to embarrass them with pornography.

They’re spied upon 24/7.

Your film raises questions about the church’s tax-exempt status. Sen. Ron Wyden is pushing to re-examine that classification by the IRS. How realistic is it that something could change?

AG: I think it’s realistic. I think it depends on the willpower.

If somebody like Sen. Wyden or others have sufficient willpower, and see what a terrible thing it is that all of us American citizens are effectively subsidizing these ongoing abuses, then maybe there will be the will to do something about it.

I’m fairly certain that a diligent investigation into the Church of Scientology would reveal that it’s not being run as a religion. It’s being run as a business.