A lot of the current research focuses on "trust" inside groups. This is not exactly double-blinded climate controlled stuff, as you might expect, just brave and smart social psychologists doing their best. I find it highly plausible and confirmatory of many centuries of non-scientific observations about insularity. Disclaimer: I AM NOT SAYING DISTRUST OF PEOPLE OF OTHER BELIEF SYSTEMS IS GOOD, JUST THAT IT HAPPENS.

Atheism associated with lack of "trustworthiness signals" by believers.

Religious in-group trust and cooperation is higher.

I know of no studies on friction over expression of religious beliefs. I do kind of take as a given that there are fewer HR complaints when everybody's got the same Sacred Heart/Darwin amphibian/Santa Muerte/COEXIST bumper sticker.

Though some obvious confounders do come to mind...

Granted that there are huge trade-offs for religious homogeneity, and I think that it's almost always a bad business decision (exceptions: semi-utopian communes? survival in Hobbesian chaos? new colonies without hope of reinforcement?) It was just an exemplary argument of a sort made less often than, you know, arguments about race and IQ.