Why would you be unfit to be president if you are an atheist?
What identifiable unfitness comes with being an atheist that can be considered presidential disqualifications?
Many would question the character and moral center of a godless heathen atheist.
The fact that someone doesn't believe in supernatural beings for which there is no evidence of their existence, and then proceeds to talk to them and configure one's life habits and behaviors to what one imagines they have been instructed
hardly makes the non-believer suspect in character and morality.
Hell, the guys who flew planes into the towers were probably more religious than you are.