Novelist Anne Rice’s surprise post last week on Facebook — she announced she had quit Christianity “in the name of Christ” because she’d seen too much hypocrisy — brought cheers and smug smiles from critics of institutional faith, and criticism and soul-searching among believers.

But there’s something more at play here than one of America’s most famous Catholics — Rice re-embraced the faith of her youth in 1998 and published a memoir just two years ago, “Called Out of Darkness: A Spiritual Confession” — walking away from the church.

Rice is merely one of millions of Americans who have opted out of organized religion in recent years, making the unaffiliated category of faith the fastest-growing “religion” in America, according to a 2008 study by the Pew Forum on Religion & Public Life.

The Pew report found that 1 in 6 American adults were not affiliated with any particular faith. That number jumped to 25% for people ages 18 to 29. Moreover, most mainline Protestant denominations have for years experienced a net loss in members, and about 25% of cradle Catholics have left their childhood faith, the study showed.

And in a 2008 study by Trinity College researchers, 27% of Americans said they do not expect a religious funeral.

American Christianity is not well, and there’s evidence to indicate that its condition is more critical than most realize — or at least want to admit.

Pollsters — most notably evangelical George Barna — have reported repeatedly that they can find little measurable difference between the moral behavior of churchgoers and the rest of American society. Barna has found that born-again Christians are more likely to divorce (an act strongly condemned by Jesus) than atheists and agnostics, and are more likely to be racist than other Americans.

And while evangelical adolescents overwhelmingly say they believe in abstaining from premarital sex, they are more likely to be sexually active — and at an earlier age — than peers who are mainline Protestants, Mormons or Jews, according to University of Texas researcher Mark Regnerus.

On the bright side, Barna’s surveys show evangelicals (defined by Barna as a subset of born-again Christians, which he sees as a broader group with more flexible beliefs) do pledge far more money to charity, though 76% of them fail to give 10% of their income to the church as prescribed by their faith. Various studies show American Christians as a whole give away a miserly 3% or so of their income to the church or charity.

“Every day, the church is becoming more like the world it allegedly seeks to change,” Barna has said.

Barna isn’t the only worried evangelical. Christian activist Ronald J. Sider writes in his book, “The Scandal of the Evangelical Conscience”: “By their daily activity, most ‘Christians’ regularly commit treason. With their mouths they claim that Jesus is their Lord, but with their actions they demonstrate their allegiance to money, sex, and personal self-fulfillment.”

How to explain the Grand Canyon-sized gap between principles outlined in the Gospels and the behavior of believers? Christians typically, and rather lamely, respond that shortcomings of the followers of Jesus are simply evidence of man’s inherent sinfulness.

But if one adheres to the principle of Occam’s razor — that the simplest explanation is the most likely — there is another, more unsettling conclusion: that many people who call themselves Christian don’t really believe, deep down, in the tenets of their faith. In other words, their actions reveal their true beliefs.

That might explain why Roman Catholic bishops leave predator priests in ministry to prey on more unsuspecting children. Or why churches on Sunday mornings are said to be the most segregated places in America. It also would explain why most Catholic women use birth control even though the practice is considered a mortal sin.

Culturally, America is still a Christian nation. The majority of us still attend church at least occasionally, celebrate Christmas and Easter, and pepper our conversations with “God bless you” and “I’ll be praying for you.”

But judging by the behavior of most Christians, they’ve become secularists. And the sea of hypocrisy between Christian beliefs and actions is driving Americans away from the institutional church in record numbers.

Some, such as Anne Rice, are continuing their spiritual journey on their own, unable to reconcile the Gospel message with religious institutions covered with man’s dirty fingerprints. Others have stopped believing in God. Those with awareness who remain Christians are scrambling to find ways, like St. Francis of Assisi, to rebuild God’s church.

But remember, St. Francis offered a radical example during a time when the institutional church had grown corrupt and flabby. He was a wealthy young man who took a vow of poverty and devoted himself to the poor. His motto: “Preach the Gospel at all times — and when necessary use words.”

A well-informed hunch says American Christians aren’t ready for the kind of reformation that will realign their actions with biblical mandates. And in the meantime, the exodus from the church will continue.

William Lobdell, a former Times staff writer, is the author of “Losing My Religion: How I Lost My Faith Reporting on Religion in America — and Found Unexpected Peace.”