That whole Dr. Laura letter has a really interesting back-story.
http://www.snopes.com/politics/religion/drlaura.asp
It seems it has been doing the rounds, in one form or another, since around 2000, and has been attributed to several different authors - the most common attribution being to a James someoneoranother, who has denied being the author. Others have stepped forward, and as Chris points out with his link, it inspired a rather good segment in the West Wing.
As to the Atheism vs Christianity debate - Not sure that you can draw the conclusion that there are more non-believing ABers than believing ones based upon what gets posted in R&S. Only those committed to arguing about faith will post - that does not fairly reflect the majority of the AB population necessarily.
For myself, I dislike the fundamentalist and extremist end of religion and what it condones. I dislike the rejection of science and fact in favour of ideology, and the way religion is taught in schools. I dislike evangelising posts particularly, so will argue the toss.
I have no issue if an individual wishes to follow a religion, or whose life is improved through their faith, so long as they do not insist that their beliefs are worthy of automatic respect or deference, or that our society should be shaped and guided by deference to religious observance, or that the religious should be seen as the moral lodestones of our society...