By Dan Merica, CNN

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Washington (CNN) – The Christmas season is revealing a growing rift among American atheists when it comes to the question of how to deal with religion.

Some atheist activists are trying to seize the holidays as a time to build bridges with faith groups, while other active unbelievers increasingly see Christmas as a central front in the war on religious faith. With the dramatic growth of the nonreligious in the last few decades, more atheist leaders are emerging as spokespeople for atheism, but the Christmas rift speaks to growing disagreement over how atheists should treat religion.

On the religion-bashing side, there’s David Silverman, president of the group American Atheists, which raised one of its provocative trademark billboards in New York’s Times Square last week. “Keep the MERRY!” it says. “Dump the MYTH!”

The sign features a picture of a jolly Santa Clause and another of Jesus dying on the cross – a not-so-subtle attack on Christianity.

“Christianity stole Christmas in the first place and they don’t own the season, they don’t own the Christmas season,” Silverman said, pointing to pagan winter solstice celebrations that predated Jesus Christ. “When they say keep Christ in Christmas, they are actually saying put Christ back in Christmas.”

The New York billboard, which will be up until early January and is costing the group at least $25,000, is the latest in a long line of provocative American Atheists signs, which attacked then-Republican presidential nominee Mitt Romney’s religion during this year’s presidential campaign.

It’s not the only way Silverman is using Christmas to attack Christianity. In a recent TV interview with Fox News’ Bill O’Reilly, he said the American Atheist office be open on Christmas Day and called for an end to Christmas as a federal holiday.

O’Reilly, in turn, called Silverman a fascist.

Despite Silverman’s knack for making headlines, however, other prominent atheists are putting a softer face on the movement, including during Christmastime.

“I just think the whole war on Christmas story is bizarre” said Greg Epstein, the Humanist Chaplain at Harvard University, who has emerged as another spokesman for the burgeoning atheist movement. “I think that any atheist or humanist that is participating in that story needs to find better things to do with their time.”

From his point of view, atheism and religion can happily coexist, including at the holidays.

At the chaplaincy, Epstein has reached out to local religious groups, packaging holiday meals and breaking bread with believers to discuss their similarities and differences.

Sponsored by the Humanist Community at Harvard, evangelical Christians, Jews, Buddhists and Zoroastrians, along with a number of atheists, were among those represented at a recent meal packaging event for hungry kids in the Boston area. Around 250 people participated and over $10,000 was raised – including donations from local Lutheran and Methodist churches.

Epstein calls this sort of inter-religious dialogue “healthy.”

“We as a community need to be about the positive and we have so much positive to offer,” he said. “I think that we really can provide a positive alternative to religious holidays that are not meaningful because of their religious content.”

Silverman, for his part, is more than comfortable being negative when it comes to religion.

“We should look at the results - people are listening to us because we are shouting,” he said. “They don’t hear you unless you shout. … Sometimes you have to put political correctness aside. We need to get louder. I believe we are seeing the fruits of that volume.”

As proof, American Atheists points to the way their donations skyrocket after every billboard campaign. “We get donations and memberships because we are taking the stand that we do,” said Silverman, who would not give specific numbers on fundraising. “The donations are flowing in right now. People are loving it specifically because of the billboard.”

Epstein would rather see more emphasis on volunteerism, though he acknowledges that some atheists are drawn to Silverman’s vocal model. Both men said they appeal to different parts of the atheist movement.

“We are GOP and Dem, man and women, black and white – the only thing that holds us together is atheism,” Silverman said. “A movement like ours needs all sides. It needs people who are working to be conciliatory and it needs people who are willing to raise their voices.”

Religious “nones” – a combination of atheists, agnostics and the religiously unaffiliated, have been growing their ranks in recent years. According to a Pew Research study released this year, the fastest growing "religious" group in America is made up of people with no religion at all as one in five Americans is not affiliated with any religion.

The survey found that the unaffiliated are growing even faster among younger Americans. According to the poll, 34% of “younger millennials” - those born between 1990 and 1994 - are religiously unaffiliated.

Though not monolithic, younger atheists, according to Jesse Galef, communications director of the Secular Student Alliance, are more prone to celebrate a secular version of Christmas than to ignore the holiday.

“I am very much in favor of celebrating the secular Christmas,” Galef said. “It is a celebration of the spirit of giving and I think religious divisiveness goes against that effort.”

Other atheists celebrate Festivus, a December 23 holiday meant for atheists looking to celebrate during the winter without participating in a Christian holiday. The holiday, which entered into popular culture through the television show “Seinfeld” in 1997, has gained popularity in recent years.

At the Secular Student Alliance office in Columbus, Ohio, the staff will play Secret Sagan, a nod to the famed scientist, instead of Secret Santa. And instead of Christmas decorations, they put up a Winter Solstice Tree with ornaments from the movie “When the Grinch Stole Christmas.”

“We celebrate the holiday season, just not the religious holiday,” Galef said.