Commuters in Washington, D.C., and London encountered a public debate of sorts between atheists and Christians during a December ad battle on city buses.

"Why believe in a god? Just be good for goodness' sake," read D.C. ads sponsored by the American Humanist Association (AHA). "Why Believe? Because I created you and I love you, for goodness' sake. —God," responded ads from the local Center for Family Development.

In London, the British Humanist Association's ad campaign — "There's probably no God. Now stop worrying and enjoy your life" — was countered by "Crunched?" ads citing Luke 2's Bethlehem pronouncement. They were produced by MEMO, a Christian organization displaying Scriptures on British public transport since 1883.

The advertisements, which are spreading to Barcelona and Toronto but were barred in an Italian city, are just one of several recent marketing efforts from atheist groups often critical of Christian evangelistic efforts.

"Atheistic attacks on Christianity have occurred throughout the ages," said Jerry Root, assistant professor of evangelism at Wheaton College. "These buses are the places where the modern debate seems to be occurring with a 'bumper sticker' flare."

Observers question whether marketing techniques traditionally used to sell consumer goods and services will be as successful at selling belief systems. And they point to the ironies inherent in atheist proselytizing.

Atheists say evangelism is not their goal. "We are not preaching to those who don't think like us," said Fred Edwords, AHA communications director. "All we are trying to say is, 'Hey! We're over here.' "

Many Christian leaders are also wary of calling the bus ads evangelistic. "The atheists understand that the minds of people are captured by persuasion," said Ron Forseth, vice president of Outreach, Inc. "In that sense, it is evangelism. But it's not evangelism in the sense of 'Good News,' though many of the platforms of persuasion are the same ones churches use."

Semantics aside, is public advertising really effective in wooing others to faith or non-faith? According to many Christian leaders, the answer is no.

"These kinds of ads are not effective — for Christians or for non-Christians," said Krish Kandiah, executive director of Churches in Mission for the Evangelical Alliance U.K. "The best these ads can do is signpost people to have a conversation."

Forseth agrees: "I highly doubt a single person has come to Christ because he or she saw a Christian fish swallowing a Darwinian dog."

Edwords said the ads are doing what the AHA hoped they would do: increase the group's visibility. "We can't imagine people changing religions after two seconds of reading a bus ad," he said. "But in this culture, we need to be interesting in order for like-minded people to see we are out there." The result: 800 new members in December.

Christian observers believe such atheist marketing campaigns can produce fruit for the church as well. MEMO received over 300 text responses to its 2008 ads.

"We are not against the atheist campaign … as we believe it will be used by God to challenge some to consider if there is a God," said Peter Day, manager of MEMO. "For most people, coming to faith is a process, not a Damascus Road experience. … A Scripture text seen on a bus or anywhere else can be part of their journey to faith."

"Christians often spoke into a vacuum about their faith, but now we have a position to contradict," said Martin Johnson, communications manager for the Bible Society in New South Wales, Australia.

Thus the response of JoEllen Murphy, the Virginian mother who created the D.C. Christian counter ad. "We are increasingly bombarded with anti-Christian messages,"

she said. "These counter ads provide a way everyday Christians can enter the debate."

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