I think we all know why the myth persists. This might be wishful thinking but maybe Peter Manseau’s new book One Nation, Under Gods will persuade some who are not familiar with the history that this is not a Christian nation. Here is an excerpt from Laura Miller’s review of the book:

“The Pilgrims might have all called themselves Christians, but some differences among them were seen by their theocratic leaders as profound threats to the spiritual survival of the community. Both Williams and Hutchinson were cast out and created communities of their own. There was literally never a point in the history of the colonies or the U.S. when all or most Americans genuinely shared the same faith. ‘The true gospel of the American experience,’ Manseau writes, ‘is not religious agreement but dissent.’”

No, America Has Never Been a Christian Country — Why Does the Myth Persist? | Alternet.