I'm reading this interview with John Marks about his new book Reason to Believe. He talks about the experiences he had the led him to abandon his Faith -- he said "I'd been through this whole experience of trying to hold on to the faith, and at that moment, whatever was left just collapsed."
It reminded me of a time when I was on a biology field trip to Hocking Hills State Park in Ohio. We were walking through a beautiful canyon with rocky walls covered with ferns and bryophytes. Small waterfalls cascaded in from the sides and flowed into a stream along the bottom of the canyon that wound along and over small cataracts of falls that cut through the sedimentary rock. It was a beautiful and breathtaking experience to walk through the forest, see the dappled sunlight reflecting on the canyon walls, and listen to the sounds of water and birds. One student asked "How could you look at this and not believe in God?" My immediate reply was, "How could you look at this and believe in God?" He saw the beauty of God's creation whereas I saw the evidence of natural processes acting over millions of years to form the sedimentary rocks, erode them away, and evolve the plants that covered them and surrounded us.
Looking back, I reflect that we were both wrong. I've come to believe that we must be suspect of any experience that confirms or denies our belief in God. Faith is an a priori belief that is a lens through which all experience is viewed. If you believe in God, you'll see evidence to support that belief everywhere. If you don't, you won't. There isn't any experience you can have that can bear on the fundamental questions.
The real issue is how we come to those a priori beliefs in the first place. Most people are indoctrinated by their parents and by the community around them. It seems only a very recent phenomenon for most people to see the vast range of ways in which religious indoctrination happens in different communities around the world. Unless you are prepared to be extremely ecumenical, we are all atheist with respect to most religions. Is there any experience we could have that would make us believe in Poseidon? And if we had such an experience, could we trust it?