Study here - https://www.nature.com/articles/s41562-017-0151
Its conclusion states:
Religions underpin large-scale intragroup cooperation 3 , but they also promote distrust of non-believers 13,19 who are excluded from such religious moral communities 3,24 . Does rising secularism 14,31 moderate effects as atheist norms become stronger within societies? The present findings suggest that intuitive moral suspicion of atheists is culturally widespread, though not universal. Given that intuitive anti-atheist biases may transfer across moral domains 19 (Supplementary Studies S1 and S3), the resilience of moral prejudice against atheists reveals a potential barrier to the full acceptance of this growing segment 31 of the global population. Consistent with predictions derived from cultural evolutionary theories of religion and morality 5 , extreme intuitive moral distrust of atheists is evident globally, among believers and atheists in both religious and secular societies. Even as secularism reduces overt religiosity in many places 14 , religion has apparently still left a deep and abiding mark on human moral intuitions.
I've not thought of things like 'moral suspicion of athiests' before, although it must underpin the regular accusations of 'militant atheism' by various organised religious groups against secularism and secularists.