When pastors gaze out from their pulpits, they may want to imagine what would happen if they asked their flocks to respond to this statement: "As long as it's between consenting adults, any kind of sex is fine."

If this were a conservative or nondenominational Protestant church, the active, "practicing" members would be sharply divided, according to a new Barna Group survey. Nearly half -- 46 percent -- would affirm this live-and-let-live approach to sex outside of marriage, while 40 percent would disagree "strongly" and 12 percent "somewhat."

There are the active members, not the people who occasionally visit the pews.

"What is surprising is the way that even practicing Christians are beginning to conform to the beliefs and behaviors that are now considered normal in our culture," said Roxanne Stone, editor-in-chief at Barna. "The big story here is that people no longer agree when it comes to the purpose and meaning of sex -- including in our churches. Many no longer connect sex and marriage the way they used to."

When looking at broader trends, this study found the usual evidence that older Americans -- the "Elders" and "Boomers" -- have much more traditional views of sex and marriage than members of the younger "Gen-X" and "Millennial" generations. Rising numbers of young Americans view sex through the lens of self-expression and personal growth, with few ties that bind them to institutions and traditions.

"What people are saying is that sex is about two people loving each other and experiencing intimacy, but you don't really need to have the word 'marriage' involved in this discussion," said Stone, in a telephone interview.

"It's surprising how quickly some of these changes have become part of what is now considered normal. … Normally, these kinds of radical changes in a culture evolve over time. But, sociologically speaking, Woodstock wasn't that long ago."

In another question, Barna asked participants if they could affirm this statement: "Marriage is a covenant before God between a man and a woman." Among "Elders," 61 percent said "yes," along with 54 percent of "Boomers" and 52 percent of "Gen-Xers." Only 42 percent of younger Millennials said "yes." "Practicing Christians" were 12 times more likely to affirm this belief than people claiming "no faith."

Another question allowed adults to give multiple opinions of the belief that "sex should only be within a marriage between a man and a woman." Popular answers in all generations included "moral," "good," "healthy," "right" and "unrealistic." However, Millennials were half as likely to say "moral" than Elders. Also, "anti-gay" was one of the top five opinions voiced by Millennials.

While these new numbers showing the shift away from marriage and traditional doctrines were not surprising -- since similar trends have appeared in similar polls of young and religiously unaffiliated Americans -- Stone said she was surprised by the degree to which these changes are now affecting people in pews.

Take, for example, other results for that "consenting adults" question. The Barna team found that "practicing" Catholics were as divided as conservative Protestants, with 24 percent agreeing "strongly" and 23 percent agreeing "somewhat" that "any kind of sex is fine" between consenting adults of whatever gender. Meanwhile, 24 percent of these Catholics disagreed "somewhat" and 28 percent disagreed "strongly."

A similar division -- close to 50-50 -- was seen among active members in liberal, or "mainline," Protestant denominations.

It's crucial, said Stone, for religious leaders to understand that young Americans are growing more and more individualistic, which makes it harder for them to affirm traditional moral doctrines about what is right and wrong on sexuality questions. It's especially hard to render negative judgments on the decisions of others.

Young Americans "are saying, 'This is my story. This is my life. This is how I choose to live it.' … But it's not just that people's beliefs have changed. Lifestyles have changed. The details of people's lives have changed," she said.

When it comes to sex and marriage, added Stone, religious leaders will need "some very robust reasons to tell young adults why they are supposed to live a radically different, truly counter-cultural life -- why they should try to live a life that is completely different from their peers and from what the culture is now saying is normal."