Do religious people repeatedly reject temptation in general? If not, would this not make religious people less trustworthy, since one cannot predict their future behaviour, and would make expecting moral behaviour from such people also another such bias.
Is striving towards a challenging ideal superior to ignoring that ideal or paying it lip service?
If you think it through the answer to your question coupled with the answer to mine provides a framework for understanding the outcome data presented upthread (the differing level of wellbeing reported by the very religious, the 'moderately' religious and the unaffiliated).
Getting back to the "cognitive bias" part, I think we have established that religious groups can:
a) Reject another group because it doesn't understand that group, even though the other group has never committed an offence against them
b) Do not reject their own members, even though they commit the offences that they attribute to the out-group.
This is a cognitive bias - seeing the world in a way that does not reflect reality.
Given that this cognitive bias can lead to conflict, is it not certain that in this case a religion which encourages members to ignore reality will cause conflict, reducing members quality of life and enjoyment?
I think a more general case could be made that dogmatic beliefs that do not match reality are a recipe for conflict.