The basic tenet of the foundation of the US was for religious freedom, whether you are Baptist, Methodist, Catholic, Muslim, whoever, this nation was set up for people to worship how they want.It's claimed by many that atheism is a religion, and therefore deserves no more consideration than other faiths in the legal arena. I would agree with that assessment. A public school may not have an Athiests Club if it disallows other religious groups, and vice versa.
You can't have it both ways though. If atheism is a religion, then belief in God is also a "religion", and the words "One Nation Under God" are a religious affirmation.
-Eric
Religious affirmations are not unconstitutional, not even when made by Congress (who are only prohibited from making laws establishing religion, or laws prohibiting the free exercise thereof. They're also the only body prohibited from doing so by the BOR.). An affirmation is not an establishment.