Christian Missionary, Daniel Everett, went to the Pirahã tribe to help "save" them and make them Christians and translate the Bible into their language. In the end they convinced him of the fallacy of religion.
Sadly this video is just a book reading with a slideshow playing over it. If one wants more here is a talk by him: http://www.youtube.com/watch?v=BNajfMZGnuo
but doesn't discuss the story in as much detail, although the full speech at Flora might.