Is the idea of a naturally-knowable and universally-binding law of right and wrong (i.e., a “natural law”) sustainable in the face of the widespread moral disagreement we see around us today? What should we say about the fact that human reason seems to have ceased delivering commonly acceptable answers to our moral questions? Is it premature to announce the epistemic death of the natural law?
Joseph Ratzinger said famously in 2002 that moral reason seems to have a “wax nose”; it can be “pointed in any direction, if one is clever enough.” What happened? Ratzinger’s answer is that the West lost its faith. Christian rationality gave way to the reason of the Enlightenment (“secular rationality”): “With the crumbling of the fundamental Christian consensus…all that remained was a naked reason that refused to learn from any historical reality but was willing to listen only to its own self… [Reason] became blind.” 1
The Orthodox Metropolitan Hilarion of Volokolamsk of the Moscow Patriarchate said something similar recently  at a symposium in London:
Beginning with the Age of the Enlightenment, political and philosophical thought has taken the direction of breaking with its Christian roots. Having extracted from the Christian tradition the doctrine of freedom, the enlighteners have laid down the vector of development which has led today to the abolition of Christian morality as such. Concern for human dignity, understandable in an age of absolutism and tyranny, has led over the centuries to the creation of the legal and social mechanisms for the encouragement of a sinful way of life.
Both the Pope and the Metropolitan see the denial of Christian faith as directly related to the moral confusion we see around us. T.S. Eliot, Russell Kirk and Malcolm Muggeridge each noted the correlation in the last century; and Dostoyevsky commented on its relevance in the 19th century 2.
Western ethical tradition has defended the idea of a natural moral law since before Plato and Aristotle. And Christian philosophy since Aquinas has made it a central part of its defense of moral principles. Yet if there is a natural moral law—a law of reason, universal in scope and binding on all people—then we would expect to find among sincere people if not universal agreement, at least widespread agreement on such important matters as the nature of marriage and the inviolability of innocent human life.
But what we actually find is widespread disagreement among sincere people over the most important practical precepts; and many people even reject the conception of a natural law altogether.
This gives rise to a dilemma. Either the traditional conception of the natural law is mistaken, or there’s another way to account for widespread moral disagreement. Aquinas accounts for it by saying that people’s awareness of the demands of the natural law can be blotted out by evil opinions, perverse customs and bad habits; in other words, sin can blot it out from people’s hearts 3; sin first, then moral blindness.
If the prophet Hosea had appeared to St. Thomas on his deathbed in 1274 and told him that a day will come when the peoples and nations of Christian Europe will strike from their memory the faith that made them great; and so too will the natural law be blotted from half their hearts; I expect he would have replied serenely: “What else would you expect?”
1 See Joseph Ratzinger, Values in a Time of Upheaval (San Francisco: Ignatius Press, 2006), 27, 43, 65-67; Turning Point for Europe? The Church in the Modern World: Assessment and Forecast (San Francisco: Ignatius Press, 1994), 28-29; Joseph Ratzinger, The Beauty and the Truth of Christ, “Message to Communion and Liberation Meeting in Rimini, August 24-30, 2002
2 T.S. Eliot, “Notes towards the Definition of Culture,” in Christianity and Culture (San Diego: Harcourt Brace & Co., 1976), p. 87. Russell Kirk, “Civilization without Religion?” The Heritage Lectures (Washington, D.C.: The Heritage Institute, 1992). Malcolm Muggeridge, “The Great Liberal Death Wish,” Imprimis, Vol . 8, No . 5 (May 1979), p. 5. Dostoyevsky, Letter to N.L. Ozmidov (1878), Dostoyevsky, Selected Letters of Fyodor Dostoyevsky, eds. J. Frank and D.I. Goldstein (New Brunswick: Rutgers University, 1987), 447.
3 Summa Theologiae, I-II, q. 94, a. 6c & ad 1.