The God Delusion- Part 3: Beliefs of the Founding Fathers

The God Delusion then goes onto discuss from the quotes gathered by Dawkins and the readings gathered from the Founding Fathers of the United States that the Founding Fathers were fundamentally not Christians.  This seems like a random argument in light of a book trying to prove that God does not exist.  What is the point of proving that certain specific individuals who are assumed by most people to be followers of Jesus Christ are really deists as presented by some or atheists as argued by Dawkins in a book seeking to proved that the existence of God truly is a delusion?  The existence of God is not contingent on the beliefs of the Founding Fathers of the United States of America.