Immoral people who commit violent crimes are often assumed to be atheists. This view appears to be shared by religious and atheist people alike, suggesting that prejudice against atheists remains strong despite the stark decline in religiosity observed in past decades in many societies.

For centuries, people have thought that acting in a moral way depended on people having religious beliefs. Everywhere around the globe, morality and religion have long been seen as intrinsically linked.

For instance, as far back as antiquity, Plato addressed in his writings the question of whether morality could be properly defined without reference to the divine. The ancient Chinese philosopher Mozi argued for his part that belief in ghosts was necessary for moral restraint.

Even in today's more secular cultures, this prejudice against atheists still persists, as a study published in Nature Human Behaviour has now shown.

Atheists themselves assume that perpetrators of extremely immoral actions are more likely to be atheists than religious believers.

Immorality and atheism

The researchers tested the perception of a link between immorality and atheism in more than 3,000 people from 13 countries around the world. Some of these people came from very religious societies, such as India or the United Emirates. Others came from more secular societies such as China, Australia or the Netherlands.

Participants were given a description of an immoral person committing horrible crimes – first torturing animals and then killing people just for the thrill of it.

Half of the study subject were then asked whether it was more likely that the perpetrator was a teacher with religious beliefs, or a teacher with no religious beliefs. The other half was asked whether it was more likely that the perpetrator was a teacher with religious beliefs, or simply 'a teacher', with no reference to religion.

Analysing the participants' answers, the researchers discovered that participants - both atheist and religious - were almost twice as likely to believe that atheists are responsible for extreme immorality, relative to believers.

"Our results offer strong evidence of extreme intuitive moral prejudice against atheists. Participants intuitively assume that the perpetrators of immoral acts are probably atheists. These effects appeared across religiously diverse societies, including countries with Buddhist, Christian, Hindu, Muslim and non-religious majorities," the authors write.

The study confirms that there is a long-standing, culturally widespread prejudice against atheists. This is evident even in societies were religion has greatly declined - atheists themselves readily associate immoral actions with atheism.

The authors suggest that this resilience of moral prejudice against atheists could be potential barrier to the full acceptance of this growing segment of the global population, fuelling discrimination against non-believers. "Even as secularism reduces overt religiosity in many places, religion has apparently still left a deep and abiding mark on human moral intuitions," the authors conclude.

In a comment piece in the same issue of the journal, Adam Cohen and Jordan Moon from the Department of Psychology at Arizona State University say that the study marked an important advance in explaining the prevalence of anti-atheist attitudes.

"Traditional social psychological theories tend to focus on prejudice as a function of group membership. In this view, prejudice toward atheists should be prevalent mainly among believers. The cultural evolutionary framework utilised here departs from this approach, proposing that distrust of atheists is rooted in intuitions that religion is necessary for moral behaviour," they wrote.