Separation of church and state is not complete nonsense. There is a middle ground. The founders were on both sides of this controversy.
Founder opinions mattered less than the contract that was crafted between the diverse states to form the union. Religion was off of the table at the Federal level, but most of the states had official state religions at our nation's founding. The original Constitutions of those states bear witness to what I've said. Look them up at the Avalon Project website if you need to see for yourself. The last state to disestablish was Massachusetts in 1820.
The issue began to be Federalized after ratification of the fourteenth. Took an activist twentieth court ruling to impose the bright line separation that is now the law of the land.