Seven years ago, a leaked video of an actor America was accustomed to thinking of as a good guy — a Navy aviator, a lawyer fighting a corrupt law firm, the last samurai — made his grip seem tenuous at best.

Try not to look: Tom Cruise was talking about Scientology.

“I think it’s a privilege to call yourself a Scientologist, and it’s something you have to earn,” Cruise, wild-eyed and clad in a black turtleneck, said in the video as a guitar riff droned in the background. “Because a Scientologist does. He or she has the ability to create new and better realities and improve conditions.”

For more than nine minutes, Cruise riffed on the power of his chosen faith. He spouted Scientology jargon. He laughed maniacally. Scientologists “are the authorities on the mind,” he said. “… We can bring peace and unite cultures.”

His conclusion: “Either you’re onboard, or you’re not onboard.”

Now, a new HBO documentary — “Going Clear: Scientology and the Prison of Belief,” which premiered this week at Sundance — takes a look at some of the consequences of not being onboard.

Based on an exhaustively researched — and exhaustively lawyered — book by Lawrence Wright of the New Yorker, “Going Clear” presents many of the most damning claims about Scientology, a much-disputed religion  founded by L. Ron Hubbard possibly as a result of a bar bet.

Among the film’s allegations:

  • The church abuses its members. In the film, Spanky Taylor, an ex-Scientologist and John Travolta’s former publicist, said she was forced to do hard labor while pregnant, and that her baby was taken away from her by the church for a time. Punishments for those who doubted included sleep deprivation. “You’re so thoroughly indoctrinated, deluded and not questioning anything because [Hubbard] had all the answers,” said Taylor, as USA Today reported. “So you continue to believe all the nonsense.”
  • Scientology broke up Cruise and Nicole Kidman because David Miscaviage, the church’s leader, did not care for Kidman’s father, a leading psychologist in Australia. As Cruise himself made clear in a notorious 2005 interview on the “Today” show, Scientologists do not approve of psychology.
  • The church won’t let John Travolta go — and is keeping the actor hostage with a “black PR” file, as People reported. “Very often they’re smeared,” Alex Gibney, the film’s director, told Variety. “Very often people they work with get letters denigrating them, sometimes trying to embarrass them with pornography. They’re spied upon 24/7.”

The Church of Scientology released a full-page ad in the New York Times and a statement ahead of the Sundance premiere, calling the film “Rolling Stone/University of Virginia redux.”

“Despite repeated requests over three months, Mr. Gibney and HBO refused to provide the Church with any of the allegations in the film so it could respond,” it said. “Their sources are the usual collection of obsessive, disgruntled former Church members kicked out as long as 30 years ago for malfeasance, who have a documented history of making up lies about the Church for money.”  The church referred those interested in its side of the story to the Web site freedommag.org/hbo.

“I chose to make this film because I think it’s an important topic,” Gibney told Reuters. “Not only about this church of Scientology, which everybody’s fascinated with partially because of the celebrities, but partially because of the way that the church seems to turn people to do things that I think they would normally never do if had they not entered the church.”

For Gibney and the author of “Going Clear,” this religion can turn its adherents into monsters.

“You’ll see a lot of good people in this movie that were drawn into Scientology and then to have them transformed into people that they didn’t recognize,” Wright said. “… That process of belief and inculcation of behavior tells us a lot about human nature.”

Challenged by the litigious church at every turn, the film took a cadre of lawyers — 160, by USA Today’s count — and extra security to get to the festival.

“I want to emphasize what a tremendous amount of courage it took for people to come out,” Wright said of the former Scientologists who appeared in the film. “The goal was to get as many people to talk so they’d feel safe in numbers.”

“Going Clear” premieres on HBO on March 16.