I have been having very similar discussions with the Jehovah's Witnesses for over 10 years. They keep bringing me more 'evidence' and I keep finding more 'questions'. Humans have a way of finding proof of what they believe, but ultimately it comes down to making a personal choice about how we wish to explain that which (at this point in time) cannot be explained, let alone understood.

I had 3 young Mormons visit me one day and I asked them a simple question: Would you still be a Mormon if your parents were not Mormons? All 3 fell into silence and then had to suddenly leave. I doubt they had ever considered such an option. It is common to grab hold of something that is easy to grasp and hang onto it if it 'works' for you. It is less common to dig deeper and question why we need to believe in something.