In the US, religious people are more racist than average. Tom Rees at Epiphenom explores possible explanations for this, drawing from a few studies. Most crucial, it seems to me, is that it doesn’t seem to be the faith aspect of religion that creates the tendency. It’s the social conformity. Furthermore, this correlation seems to have declined over the past 40 years.
So lots of people are religious in large part as a way to fit in with their communities. It makes sense that people overly concerned with conformity in a community would be more suspicious of people who are different. It also makes sense that as social attitudes harden against racism, those concerned with conformity would also feel an incentive to be more racially tolerant.
I think it might be interesting to explore other attitudes that are like racism when it comes to suspicion of outsiders but not as socially taboo. (Homophobia perhaps? Distrust of foreign governments?)
Racism is particularly linked to fundamentalist religion. Rees thinks that this racism is an expression of an increased amount of right-wing authoritarianism, which he doesn’t strictly define. He does give us this:
They found that three key beliefs about how the world works seemed to mediate the relationship between fundamentalism and authoritarianism: certain knowledge (the idea that there are fixed, absolute truths), simple knowledge (the idea that the world is simple and straightforward, not complex), and omniscient authority (the idea that authority should be obeyed).