It's only a debate by those that want religion banned
And the founding fathers were religious majority Christian
And they clearly didn't found this country on Christian principles as much as you want to believe that. They directly state that again and again whether it is Thomas Jefferson's letter stating there should be a wall between religion and the state, Jefferson using the word Creator instead of God (a clear signal of Deist beliefs), the Treaty of Tripoli which was signed by John Adams and is on par with the Constitution stating the United States was not founded on the Christian religion, etc.
No one wants religion banned. Some have poked fun, but no one has said you can't practice your religion. The only issue people have had is making laws based upon religion instead of the constitution.