You did, by default.
Without a commitment to the transcendent there IS no concept of "natural rights."
You quote Lewis to propose ANY morally based constraint is bad, when that is, like anything else touched by the libertine, a corruption of the intended good.
I already conceded a religious government without limits is like the Taliban. You keep fighting, because you correctly infer your position is inherently dissonant. You can not excise the moral without losing the sublime rights our form of government recognizes.
Religion is absolutely necessary - to inform personal morality.
A religious government without limits is like the Taliban.
What made the USA unique was that it imposed those limits upon government.
That is the essence of American conservatism - a government of limited and enumerated powers. A moral and religious people is an essential feature of this, but it is not what our government is based upon or what made it unique.