The Government is Secular; not the Nation
The Founding Fathers had a vision of a secular Government, not a secular nation or culture. Their vision of a secular government was just that, a Federal Government that was not controlled by any religious institution or organization. Their goal was not to keep religious convictions and dialogue out of the public square. They never inferred that religious convictions on morality should not inform the public or the government.
The kind of secular system proclaimed by some secularists today would involve a violation of the First Amendment which is the freedom of religion and the freedom of speech. Free men have the right to speak their mind on any subject in the public square or in private, this includes the religious and nonreligious. The very idea that people could not express their religious beliefs in the public square or in spaces that some label ‘religious free zones’ is ridiculous and would violate our First Amendment rights.
Some interesting facts; the word secular is not used in any of the Founding documents. The expression, ‘the wall between church and state’ is not found in any of the Founding documents. It was used one time by Thomas Jefferson when writing to a Baptist Church in Connecticut. There is nothing in the Constitution that would hinder states from having a State Religion. The restriction was to only apply specifically to the Federal Government.