Just a quicky. here are a couple of links on the subject of non (religious ) belief. The Huffington Post is a very very good site for thinking people who want an insight into American life, a subject of importance after all. In a large poll 15% professed non-belief, a group larger than any single denomination such as Catholics or Mormons. The group describing itself as evangelist or funamentalist seems to be a terrifying 35%. But we are looking at two groups that are not easy to compare - one group shouts louder than the other.
A very interesting figure to know would be the proportion of the religious who came to their beliefs when they were old enough to reason for themselves.