A friend on Facebook pointed me to this lecture by Rodney Stark, author of the excellent book Victory of Reason. This lecture is titled " Religious Competition"
I think most of what Stark says is spot-on. I disagree with him, of course, when He dogs the protestant movement and gives an unexcused free pass to the Roman Catholic Church.
I would also add that I believe we (believers) are all called to be priests, or religious suppliers, in the NT. So it is incumbent on us to be well equipped to service the markets of unbelief all around us.