In the 1960s, O'Hair successfully challenged the constitutionality of prayer in public schools, but alienated many moderates with her inflammatory rhetoric. She was kidnapped and killed in an extortion scheme in 1995.
"I think to try to shock people into it is just going to do what Madalyn did and set everyone against her," says Sellman, a graphics designer in Maryland.
Not all atheists have forsaken O'Hair's approach. This summer, Michael Newdow drew considerable public scorn for challenging the constitutionality of the words "under God" in the Pledge of Allegiance.
Sellman says she mostly keeps her opinion on religion to herself. But it can be awkward when she tells people she does not believe in God, she says. "People have actually accosted me at work … and said, 'You don't believe in Jesus?" she says. "You're looked at like some kind of nut."
"I think it's hard to be a nonbeliever in America," says Michael Shermer, the head of the Skeptics Society. "We're such a minority."
Five Percent, Say the Experts: But Many Disagree
America is one of the most religious nations in the developed world, with far more people attending church and professing their faith than in many European countries, for example.
Roughly 5 percent of the population consider themselves nonbelievers, according to numerous polls, and that number has been relatively steady over recent decades, says Rodney Stark, a professor of the sociology of religion at the University of Washington.
"I've looked at polls going back to the 1930s and, hell, nothing's changed," Stark says.
Nonbelievers tend to think that number is artificially low, however. The American Atheists believe there are about 30 million "Godless" Americans.
"People don't always give accurate answers [to surveys and polls]," says Ed Buckner, of the Council for Secular Humanism.
Buckner points to a 2001 study by the City University of New York, which found a drop in religious identification over the past decade. In 1990, the report found 90 percent of the adult population identified with a particular religious group, such as Catholic or Jewish. In 2001, that figure dropped to 81 percent.
A 2001 ABCNEWS poll found that 13 percent of respondents said they had no religion.
"I do believe the number of people without religion is growing slowly," Buckner says.
Likewise, Reginald Finley, the host of the online "Live With the Infidel Guy," atheist radio show, is convinced large numbers of nonbelievers keep their views to themselves. "I get tons of e-mails from atheists in the closet," he says.
Some experts, such as Stark of the University of Washington, are skeptical, however. "The thing that's remarkable about American religion is how durable it is," says Stark, the sociologist of religion.
"No competent study has ever shown an increase in atheism in the United States," says Darren Sherkat, a sociologist at Southern Illinois University and an avowed atheist himself.
Complicating the question is the fact that there is no clear line between believers and nonbelievers. Some people say they are religious, but do not believe in a God that oversees the fates of human beings. Others have spiritual doubts and do not belong to an organized faith, but would not call themselves Godless or atheist.
"These categories aren't so easy," says Bruce Forbes, a United Methodist minister who is also a religious studies professor at Morningside College in Sioux City, Iowa.