As someone who is a practicing Catholic and therefore knows lots of people who are not family members who also regularly attend services, I can say at least ane

As someone who is a practicing Catholic and therefore knows lots of people who are not family members who also regularly attend services, I can say at least anecdotally that tolerance and zeal for one's faith are not terribly correlated (as are intelligence and zeal, for that matter). I'm not sure about any studies, but the presence of counter-examples would make me look to confounding factors.