Halloween is coming, so here’s a tip for those of you who have yet to decide on a costume. If you really want to scare people, dress up as Richard Dawkins. Or Sam Harris.

Or just tell them you’re an atheist.

Confirming and expanding upon previous research, a newly published paper reports that, in the minds of many, atheists are deeply threatening. Specifically, they are seen as posing a danger to the value systems that unite us.

The fact that their belief systems defy the national consensus, along with “negative cultural stereotypes of atheists as cynical,” leads to the assumption that “atheists are unlikely to follow important group-based value norms” such as reciprocity and trust, according to a research team led by Skidmore College psychologist Corey Cook.

Atheists produced more "feelings of moral disgust" than other "groups also perceived to threaten values—Muslims, gay men, and people with HIV."

“The perception of threat alone is enough to drive intergroup enmity,” the researchers note, “even if atheists as a minority group do not have the political power or raw numbers to institute cultural changes in value systems.”

Cook and his colleagues describe two experiments, one of which featured 100 undergraduates at a large public university in the southeastern U.S. Seventy-three percent of participants were affiliated with a Christian church.

They were randomly assigned to read one of two news stories designed to appear as if they ran in the college newspaper. One was about a proposed expansion to the dental school. The other was about “moral decline among college students.” It reported that “traditional values such as loyalty and fidelity are less important than in previous years,” adding that today’s students lie and cheat more frequently than their predecessors.

After completing a filler task, participants reported how tense and anxious they felt when thinking about groups of people who are frequently stigmatized: college students, gay men, HIV-infected students, and atheists. They were also asked to indicate, on a one-to-six scale, “whether they would be willing to vote for an atheist presidential candidate, support a local business run by atheists, and whether they believed the U.S. Supreme Court should include atheists.”

Participants who read the neutral essay felt less anxiety when thinking about atheists than they did when considering the other feared groups. But for those who read the "moral threat" story, the level of anxiety provoked by pondering atheists shot up, to the point where it basically equaled the tension elicited by thinking about the other feared groups.

In addition, those who had read about the looming “moral threat” expressed more willingness to discriminate against atheists in the various contexts described above.

In another experiment, atheists produced more “feelings of moral disgust” than other “groups also perceived to threaten values—Muslims, gay men, and people with HIV.” Participants in this experiment (131 undergraduates) also expressed more willingness to discriminate against atheists than against member of the other groups.

Cook and his colleagues have a pretty good idea why the anti-atheist prejudice they documented is so pervasive.

“Atheists are stereotyped to be (among other things) cynical, skeptical, and nonconformist,” they write. “Individuals perceived to endorse conflicting values, or who fail to openly endorse group values, could threaten to undermine performance and success of the group as a whole by failing to adhere to group norms.”

“Although acceptance and egalitarianism are endorsed as traditional American values,” they add, “perceptions of violations to personal and group values are often seen as justification for hostile attitudes and subsequent discrimination. Such justification is reflected in the unwillingness to accept atheists as an everyday part of American society.”

So it appears atheists have a huge perception problem: People widely assume that if they reject the notion of God, they also reject essential ethical values. Although they don’t represent all atheists, it would clearly help if humanists, with their vision of a moral society that does not require otherworldly guidance or punishment, could raise their profile.