I am late to this discussion but these are my thoughts:
First, I think of psychology as an art not a science. Kind of like cooking or a medical doctor. Sure they use scientific fields to help produce an end result but the diagnostic and therapeutic/culinary presentation is based on artistic experience, not scientific methodology.
Second, I am coming at these questions as an agnostic which was not included in the opening post.
This is not a simple question. Education, upbringing, social status .... I find this question to rest in the Nurture side yet the Nature side is just as important. It comes down to this one question that none of us can answer for ourselves.
Are you an innately curious person or do you accept what others tell you as truth?
I am an agnostic so I have a hard time with this question. I have read Homers Iliad and Odyssey and yet I have no faith in the Greek Pantheon. Why are people that read or study any particular theology automatically considered a theist by Atheists? Philosophy is Philosophy.
Good luck on that private conversation heh.
The bold here seems to be either bias or directed at a specific person without any regard to a greater conversation. That's just my observation so that's all I have to say about that.
I had come into this tread late but from what I have read. ..... These requests have gone unnoticed.
To recap my view; Psychology is not a proven science to ask such a profound question based on science.
Upbringing, education, social economic status are important factors for why people "have" or "refute" faith. IMHO innate curiosity is just as if not more important a factor. That being said, being innately curious or not does not determine your level of faith or denial. Nurture determines that while Nature gives or denies innate curiosity.
I'm sorry, while reading this thread others have fallen into their tribal traps. A few of your suggested guidelines have been stepped over. Still, on the surface this is a good question. Unfortunately others have used it to build the walls of an "other".
We all have far more in common than something as silly (or as important) as "faith". Psychology is incapable of answering these questions as stated. We on the other hand can say "to each their own" or "It's my way or the highway" (overly simplistic ad hominem). All I can say is, if you have the natural gift of innate curiosity the you have the ability to understand the other side if you are so inclined.