A meta-analysis of 55 independent studies carried out in the United States with more than 20,000 mostly Christian participants has found that members of religious congregations tend to harbor prejudiced views of other races. ...In general, the more devout the community, the greater the racismAlthough the study mainly involved Christians, Wendy Wood, the lead author of the study, speculates that religion in general, rather than anything specific to Christianity, is the primary factor.
“Religious groups distinguish between believers and non-believers and moral people and immoral ones,” ... “All religions offer a moral group identity, and so across world religions — including Buddhism, Hinduism, Muslim, Judaism and Christianity — the religious ingroup is valued over outgroups.”
So basically her theory holds that religion promotes group thinking. Members of some religions tend to see themselves as part of a group that knows the truth, while everyone not of the religion is at the very least ignorant, or at worst damned. If you view the world from this sort of us & them perspective, it seems reasonable that you might be prone to group thinking in other matters, such as race.
Wood's conclusions may apply to certain religions such as Christianity and Islam, which sharply divide people into groups, but I'm not sure it holds for religion in general. What about religions that recognize multiple paths to enlightenment or salvation? I'm always wary of drawing sweeping conclusions from studies. But there is one finding that isn't at all surprising.
Her analysis found significantly less racism among people without strong religious beliefs.