I think to our Founding Fathers, freedom of conscience was closely linked to the concept of free will; in other words, the state wasn't responsible for enforcing one particular belief because that was between God and man. The state didn't need to get between them, as had been the case in King Henry the 8th's Anglican state, or the other European monarchies where the kings were provided their power from God to rule man. I'm also arguing that the Founding Fathers would have each agreed that there was an external reality no matter what their own opinions were. Disagreement and debate were prevalent in their age, proving that the truth is elusive. But they all agreed that a well-crafted set of laws which respected mankind's freedom of conscience would set us free in contrast to other political systems. In other words, the Enlightenment taught us to let faith be personal and the law be limited but based on fact and reason. But it did not teach us that facts were relative. Calculus and Newtonian mechanics would have been for others to discover, were that true.