Obviously, what God has written would be the best route, but the rest of the world does not share the same worldview as we do.
Numerous traditions merged into our founding of the country and this discussion is nothing new. How much of the Bible should be the law for all when not all believe in the Bible or even are of the elect? It was rather straight forward in Israel. If you were born of Abraham, Isaac, and Jacob you were a Jew, and thus as a Jew living in the nation you were elect and as an ethnically elected person and national citizen you were in covenant with God and thus to be ruled by the National law Code of Israel given by and through Moses.
For many years when those coming forth out of Rome came to the soils of America they fought to keep a quasi-Israelite/Romanistic system in place. Many of the Colonial Laws reflected that.
Poor ole Roger Williams was even excommunicated for teaching the gospel in a way contrary to the Puritans and Pilgrim's state church law code. Many other Baptists were too banned, even thrown in jail for their teaching that was not authorized by the state.
This set up a battle when the framers were developing the COnstituional government of America. Eventually, men like Obadiah Holmes, John Clarke, and James Randall were indicted by a Plymouth Grand Jury for meeting in houses on Sunday in spite of a court order against thos practices. They were thrown into prison. Some were even beat and whipped badly.
But through Isaac Backus and some other Baptists they got the attention of the Great Lion of Liberty, Patrick Henry, Thomas Jefferson, and James Madison and the idea of the First Amendment developed and was placed in the land's national constitution. Though it did not alter the state established religions to begin with eventually it was applied to all states through the Supreme Court of the land. The seeds began though back in the founding days.
Some feel though this trend left us with no way to implement a Godly law code in the lands. Even the great scholar Dr. Charles Hodge of Princeton Seminary in the 1800's was still trying to reconstruct the Mosaic Insraelite law for the American people. In his massive and solid 3 volume systematic work he set forth the idea that if people did not attend churches on the Sabbath that they needed to be jailed. He sought to make this a federal law for all in these lands.
But, for years another stream has been flowing into our political and civil philosophical minds over the years. it is a stream that divides the law of God into two spheres, a God to man sphere and a man to man sphere.
Men like Isaac Watts (1674-1748) and Richard Hooker (1554-1600), an Anglican, and even Thomas Aquinas (1225-1274), argued that God's law was not just found in the Mosaic code but also implanted into all at birth through a common universal conscience. It was this tradition that gained a lot of ground and even promoted strongly by the writer of our Declaration of Independence, Thomas Jefferson who said: "All men are created equal, that they are endowed by their Creator with certain unalienable rights, that among these are Life, Liberty, and the pursuit of Happiness."
The ideology there, that also was reflected in some of the other great writers that were heavily studied by our founders, writings of Thomas Paine, Montesquieu, as well as the Bible itself, the dominate, though slowing growing, thought was that America was not Israel and we were not to have a government led religion like what was and even still is in Europe today (even in its Erastianism form).
Thus the base design for our government ideology that began to shape most of the stronger currents based the idea of a government on what we call a "natural law ethic." It refers back to what our Declaration said in "natures God and Nature's Laws." As a people the founders represented that idea where "the design of civil government is the secure the person's, the properties, the just liberty and peace of mankind from the invasions and injuries of their neighbors" (Dr. Norman Geisler, in The Best in Theology, Vol. 1, p. 259).
Government thus was to be established and sustained not by the direct rule of the Bible, a product of special grace revelation for the elect, but from the realm of common grace that produced the light of conscience in all men (see John 1:9 and Romans 2:14-15).
Watts followed another great civil philosopher that shaped the days of our country in that he read and followed John Locke. In doing so he avoided the extremes of antinomianism (no law and anarchy) and and the extremes of re-constructionism or theonomists who want to enforce the entire Bible law code onto a society where not everyone is even of the elect or a believer (like Dr. Hodge wanted to do with the Sabbath even in the mid to late 1800's).
This ideology set the stage for the First Amendment, which has been touted by many civil scholars, as the greatest clause of any civil document in the world, and it based our civil law upon natural reason and common sense (to use a Thomas Paine term) with liberty for all, even for those who did not believe so long as their actions did not infringe or violate the life, liberty, or property of another.
As Dr. Geisler stated:
"
The civil law, however, does have a moral basis in what Watts called variously, 'nature,' 'laws of nature,' 'natural rights,' 'natural conscience,' 'reason,' 'principles of reason,' 'light of reason,' 'divine revelation,' 'candle of the Lord,' and 'ordinance of God.' For Watts the natural moral law includes such things as honesty, justice, truth, gratitude, goodness, honor, and faithfulness to superiors. The laws of nature also include personal duties such as sobriety, temperance, frugality, and industry. In brief they include the kinds of things addressed in the second table of the Mosaic Law (attitudes and actions towards men) but not the first table of the Mosaic Law (those toward God). These are the same kinds of things C.S. Lewis listed as part of the natural law which he found in all major cultures" (p. 260).