Thomas Jefferson, one the three deist leaning Founders, is credited by society as having defined a complete separation between church and state in the United States. The fabled “wall of separation” attributed to him is just that; a fable.
In his letter to the Danbury Baptist Association, Jefferson reiterated the Constitutional prohibition against the federal government’s ability to interfere with religion. Knowing the rights of each individual state to establish a religion for their particular state, independent of federal intrusion, Jefferson reminded the Danbury Baptist Association of his limitations under the Constitution; as president, Jefferson could not interfere in matters of religion.
At the time the First Amendment was written, seven states had their own established state religions. Each of those states eventually repealed their laws of establishment with the last holdout, Massachusetts, passing their disestablishment law in 1833.
Our lack of knowledge and understanding of the Constitution and the Bill of Rights leads us to believe in certain governmental and societal falsehoods. The reality of the constraints placed on the federal government by the First Amendment and other amendments are such that allowed the legislature in North Carolina to entertain a bill establishing a state religion (a politically laughable endeavor) in 2013. It also allows for atheist churches to be formed throughout the United States without any incursion by the federal government. However, the state legislatures can do as they please within their own states.