If God is the Author both of Scripture and of Nature --- and above all, human nature -- then there must be truth embedded IN US which shows that God's Law is real, infinitely good, and valid for everybody.
That requires more than a wave of the hand and a "Tell it, Sistuh." It requires the hard work of thinking natural things all the way through, to where they open (by God's grace) onto the possibility of contact with the Presence of God.
I agree, good article.
The flaw in your statement is the introduction of the sin of Adam which spread to all of us.