Gervais et al. Do you believe in atheists? Distrust is central to anti-atheist prejudice Journal of Personality and Social Psychology:

This paper studied (mostly Christian American) individuals' attitudes to atheists. One of the most interesting results was that atheists were the least trusted group when compared to Muslims and homosexuals. One reason put forward was that the existence of atheists threatened organised religion's ability to bring people together especially in countries like the United States:

Religion appears to be a “social glue” in the world, yet the least religious countries are actually among the most cooperative and peaceful on the planet...It is important to recognize that religious prosociality (voluntary behaviour helping others) is primarily a theoretical framework for explaining the types of beliefs that can act as motivators of human cooperation in the absence of large-scale institutions for promoting prosociality. In this view, religion may have once been—and may still be, in many places—one of the only games in town in terms of bringing people together into large cooperative social groups.

This is no longer the case in large parts of the world, and societal-level existential security (as guaranteed by many modern social institutions) is a persistent predictor of reduced religious belief. This is perhaps most evident in Scandinavia, where religious belief is largely a historical curiosity, and the state provides most vital services.

Given that religious prosociality, but not secular institutions, directly implies distrust of atheists, the aforementioned finding that anti-atheist prejudice is exaggerated in strongly religious countries becomes clearer, as these countries also tend to rely the most on religion to guarantee cooperation. Freed from this constraint, people from countries that depend primarily on secular institutions do not tend to distrust atheists.