Why do we believe what we believe, and how is it possible that we differ so much? Our beliefs comes from our senses, culture, in-group, experts, feelings and thinking. Of these, only thinking and expertise can make a defensible case. (This is a major rewrite of the original 5/19/19 post.)
Mother Jones has a really interesting article on how our beliefs block new information: Pre-existing beliefs, far more than new facts, skew our thoughts. Feelings arise before conscious thoughts and color them. Confirmation bias gives more weight to facts that match our existing beliefs. Beliefs are adjusted to match the audience.