After a wave of complaints, Des Moines Area Regional Transit buses will no longer display advertisements that acknowledge the existence of atheists in Iowa.

The ads, which said, “Don’t believe in God? You are not alone,” first went up on buses Saturday and were removed by Tuesday.

Gov. Chet Culver said he was “disturbed” by the ads.

This isn’t the first controversy surrounding atheist advertisements on buses. After an ad campaign was successful at generating publicity (and a lot of controversy) in London and elsewhere in the UK, atheists and advocates of religious freedom have attempted to replicate those efforts in many cities in the United States.

According to a Pew Research study in April, roughly 5 percent of U.S. adults say they do not believe in God, but only about a quarter of those adults call themselves “atheists.”

A 2006 survey by sociologists at the University of Minnesota found that atheists are “America’s most distrusted minority.” According to the survey, they are tolerated more on the east and west coasts than they are in the Midwest:

American’s increasing acceptance of religious diversity does not extend to those who don’t believe in a god, according to a national survey by researchers in the University of Minnesota’s department of sociology. The study will appear in the April issue of the American Sociological Review.

From a telephone sampling of more than 2,000 households, university researchers found that Americans rate atheists below Muslims, recent immigrants, gays and lesbians and other minority groups in “sharing their vision of American society.” Atheists are also the minority group most Americans are least willing to allow their children to marry.

Even though atheists are few in number, not formally organized and relatively hard to publicly identify, they are seen as a threat to the American way of life by a large portion of the American public. “Atheists, who account for about 3 percent of the U.S. population, offer a glaring exception to the rule of increasing social tolerance over the last 30 years,” says Penny Edgell, associate sociology professor and the study’s lead researcher.

Edgell also argues that today’s atheists play the role that Catholics, Jews and communists have played in the past—they offer a symbolic moral boundary to membership in American society. “It seems most Americans believe that diversity is fine, as long as every one shares a common ‘core’ of values that make them trustworthy—and in America, that ‘core’ has historically been religious,” says Edgell. Many of the study’s respondents associated atheism with an array of moral indiscretions ranging from criminal behavior to rampant materialism and cultural elitism.

Edgell believes a fear of moral decline and resulting social disorder is behind the findings. “Americans believe they share more than rules and procedures with their fellow citizens—they share an understanding of right and wrong,” she said. “Our findings seem to rest on a view of atheists as self-interested individuals who are not concerned with the common good.”

The researchers also found acceptance or rejection of atheists is related not only to personal religiosity, but also to one’s exposure to diversity, education and political orientation—with more educated, East and West Coast Americans more accepting of atheists than their Midwestern counterparts.

The study is co-authored by assistant professor Joseph Gerteis and associate professor Doug Hartmann. It’s the first in a series of national studies conducted the American Mosaic Project, a three-year project funded by the Minneapolis-based David Edelstein Family Foundation that looks at race, religion and cultural diversity in the contemporary United States.