Many Christians want to . . . pass or keep in place laws that are intended to protect notions that are central to preserving civil society. Those who do not believe that these notions should be reflected in our laws typically reply that Christians and their allies in other faith traditions have not right to legislate morality.
The constant or determined repetition of an error does not make it true. Errors are errors regardless of either their prevalence or the persistence of those who advance them. . . The assertion that you cannot legislate morality is just such a notion. No matter how often one hears that you cannot legislate morality, the truth is that you can legislate nothing else.
All laws, whether prescriptive or prohibitive, legislate morality. All laws, regardless of their content or their intent, arise from a system of values, from a belief that some things are right and others wrong, that some things are good and others bad, that some things are better and others worse. In the formulation of and enforcement of law, the question is never whether or not morality will be legislated but which [morality]. That question is fundamentally important because not all systems of morality are created equal. Some are wise, others foolish. . . For better or worse, every piece of legislation touches directly or indirectly on moral issues or is based on moral judgments and evaluations concerning what it is we want or ought to be, what it is we want or ought to produce or preserve.
When, for example, the founding fathers drafted the U.S. Constitution, they did so on the basis of competing belief systems, on the basis of competing assertions of right and wrong, which they endeavored to build to the Constitution. One or more of those belief systems permitted slavery; others did not. No side on the slavery debate at the Constitutional Convention argued that you could not legislate morality. That notion they recognized as balderdash. They knew that indeed you could legislate morality, and they intended for that legislated morality to be theirs.
Nor did any side in the struggle to legislate morality at our nation’s founding say to its opponents that trying to legislate morality was a breach of the wall of separation between church and state. Morality, after all, is not a church. They would have laughed at the confusion of mind revealed in one who thought that separating church from state meant separating morality from law. They wanted the nation to be moral. They wanted its laws to be just. But they did not want to give any one church a national legal advantage over others. They did not want the nation to be Presbyterian, Baptist, or Roman Catholic, which is a far different issue from whether or not to have ethics-driven law.
Under the Constitution the founders drafted, all persons are free to follow and to worship God. The founders enshrined freedom of religion not freedom from religion. In seeking to avoid a state-established church, they were not thereby establishing secularism or separating law from morality.
Francis, J., Craig, W., Moreland, J. (2004). To Everyone an answer: a case for the Christian worldview. Downers Grove, IL: InterVarsity Press.