Agreed! Religion, or lack there of, has no place in any professional arena. This especially includes government offices. And if someone was fired for their lack of religion, it would be a clear violation of their constitutional rights and grounds for a good law suit.
They are posted in the U.S. Constitution, in the Bill of Rights, under the 1st Amendment. You don't have to swear on a bible, you may request a non-secular swearing during court proceedings in the U.S. You don't have to pray in governmental meetings when they do. You don't have to say "under God" when reciting the pledge of allegiance. It is your right under the 1st amendment to do, or NOT do those things.
As to being fired for being an atheist, this would be simply moronic for someone to do. However, should it occur, you are protected under the first amendment and various other federal and state employment laws forbidding such an act.