The Founders did not so much assume a moral society as they understand the Constitution could only survive in a moral society. It is vitally important for the left to destroy morality if they are to end the authority of the Constitution.
In keeping with Marxist dialecticism, morality is simply a collection of practices and values designed to perpetuate the status quo. So yes, if obama and his minions are to implement their brave new world, existing morality — and the Constitution that arose therefrom — must be destroyed.