I'd add that you can be a religious believer, but still use and recognize materialist analyses of religion -- including your own religion. As an obvious and non-controversial example, any religion that finds itself widely believed in a world without central authorities is going to be pressed into service as an enforcer of oaths -- even if its founder's opinion of oaths was somewhere between jaded and openly hostile.

Are you familiar with Marvin Harris (https://en.wikipedia.org/wiki/Marvin_Harris)? I think he draws his causal arrow backwards -- it's not that a society develops ways of thinking because they'd be adaptive, it's that societies that happen to develop adaptive ways of thinking flourish -- but it's fascinating to watch his style of analysis in action, and he makes more good points than bad ones... at least if you ask me.