[AWoodside]

Meh, I think it's psychological conditioning, plain and simple. Either they've been indoctrinated to some particular faith from the time they were born, or they switch gears mentally at some point in life due to a traumatizing experience. This statement is mostly from personal experience, but I've never met a mid-life convert that just started believing for no reason. Every single one (and I've met a fair amount) convert after some traumatizing or emotionally scaring event and they turn to whatever faith is most convenient at the time and then get hooked because of the psychological comfort it provides.

My first instinct was to write that these people are simply intellectually bankrupt, irrational, and lack any semblance of personal courage, but after a few minutes of thought I don't think that's fair. I was raised Catholic and indoctrinated pretty heavily when I was young so I know first hand how effective the mental conditioning churches excel at can be. It took me a long time to remove the last vestiges of said conditioning, so I sympathize with those currently suffering from it.

I agree that in some respects the question you ask is "fascinating" but I have a feeling the answer, if we can ever satisfactorily arrive at it, will be less earth-shattering than you might hope. When I was a Christian and I knew deep down in my heart that Christianity was correct it was nothing more than the result of highly effective psychological conditioning performed on an impressionable young child. Church and Sunday school every week, prayers before bed, prayers before sleep, discussion of faith in the classroom (catholic school), threat of eternal torture for not believing, etc. etc. During this time I even had what I thought were spiritual experiences, where I heard God talking to me, but I was an imaginative kid and my experiences with God, looking back, were not qualitatively different than any of the experiences I had with any of my other imaginary friends.