Most people know that Tom Cruise is a member of Scientology. So much so in fact that, as the subject of Scientology is broached in any conversation, Cruise’s name is almost always the first to be mentioned. There have even been accusations that Scientology is to blame for Tom’s failed marriages to both Nicole Kidman and Katie Holmes, with rumors that the Scientology upper echelon has labeled both actresses as “Suppressive Persons.”

Most recently, similar rumors surround Cruise’s failure to particpate in Suri Cruise’s life, creating even greater hostility between Tom and ex-wife Katie Holmes.

It seemed nothing could pry Tom Cruise from Scientology’s grip, but now, as Mr. Cruise begins promoting his latest Mission: Impossible film, a change has come over Tom’s demeanor. Mr. Cruise is no longer as outspoken on his belief in Scientology as he once had been and one has to wonder why.

Earlier this year, a new documentary, Going Clear: Scientology and the Prison of Belief, took an inside look at what was once considered to be one of the most secretive religious organizations in today’s society, and a large portion of that critical film examined Tom’s role in Scientology. Some see Alex Gibney’s Going Clear documentary, based on the book by the Pulitzer Prize-winning journalist Lawrence Wright, as a direct challenge to Tom Cruise, as well as being an eye-opener to much of the public who had once held curiosity in Tom’s unwavering loyalty to the Church of Scientology.

The documentary did much more than to simply expose troubling practices by an organization that has struggled hard to steer away from allusions to it being little more than a brain-washing cult. Going Clear has also tarnished Tom Cruise’s once All-American image, leaving him vulnerable to criticism. Even public opinion wavered in 2005, when Tom abandoned his Hollywood publicist and filled the open position with his sister and fellow Scientologist Lee Anne DeVette.

Unlike that challenge to Cruise’s fame, the Going Clear documentary seems to demand a response from Mr. Cruise and yet he remains silent. In fact, he seems reluctant to talk about Scientology at all, not even to extol its virtues.

Meanwhile, the men behind that documentary, Wright and Gibney, are insistent that some kind of change is needed. They contend that, unless Scientology’s tax-exempt status is negated, celebrity members like Cruise and John Travolta bear a moral responsibility to speak out about the organization’s practices.

“There aren’t very many alternatives and law enforcement agencies are stymied,” Wright said in an interview. “What’s left is for journalists to call attention to what’s going on and at least inform people. We certainly are singling out some celebrities because they bear a moral responsibility and we’re making certain that they have to recognize that.”

John Travolta was more vocal, when recently asked about claims against Scientology, though he couldn’t be induced to speak negatively about Scientology.

“I haven’t experienced anything that the hearsay has (claimed), so why would I communicate something that wasn’t true for me? It wouldn’t make sense, nor would it for Tom, I imagine.”

Whether he likes it or not, Tom Cruise may have to speak publicly about his involvement with Scientology, if he expects to maintain his Hollywood star power. People want to know what’s going on and they want to hear it from Tom Cruise, himself.

“The documentary is going to have an impact on Mission: Impossible when it comes out,” says Jeetendr Sehdev, a marketing professor at the University of Southern California and a celebrity branding expert. “Secrets in Hollywood are really no longer sexy. Audiences are looking for transparency and authenticity in their celebrities more than ever before.”

Mr. Cruise’s Mission: Impossible co-star, Simon Pegg also confirmed that Tom avoids discussing Scientology, even in closed circles.

“It’s not something he talks about or preaches. I don’t know what the story is.”

What is the story, Tom Cruise?

Mission: Impossible – Rogue Nation is due for release in the U.S. and U.K. in July.

[Featured image: Tom Cruise courtesy of Michael Buckner/Getty Images for CinemaCon]