Perhaps the natural law has a proper use, and we have missed it. If the natural law does not exist to create agreement among reasonable minds on the requirements of morality for human action, then we should not be surprised when it does not.
But what is the purpose of the natural law? I believe the natural law exists to convict the sinful human heart. We can see this purpose in St. Paul’s letter to the Romans. Catholic Social Thought often quotes Romans chapter 2 for the proposition that “the law is written on the heart,” but Paul says much more about this law: “Now we know that whatever the law says it speaks to those who are under the law, so that every mouth may be stopped, and the whole world may be held accountable to God. For by works of the law no human being will be justified in his sight, since through the law comes knowledge of sin.” (Romans 3:19-20).
“Through the law comes knowledge of sin.” The Apostle Paul certainly “uses” natural law, but not to reach agreement on social policy. The Apostle Paul uses the natural law to demonstrate that we know right, yet do wrong. The standard is high and we fall short. He uses the natural law for eternal purposes, to crush any faith we may have built up in ourselves, so our faith may find rest in Christ. Is this the purpose of natural law? Can the natural law be used as a common foundation for moral reasoning, when no one lives up to the full extent of the law?
Can we expect people to consent to the rule of natural law, as a basis for State enforced social policy, when serious contemplation of the natural law illuminates our shortcomings? Or should we focus on pushing the sharp conviction of the law upon the human heart, so hard hearts are plowed, and the ground is made fertile for seeds of grace?
Is rejection of the natural law always tied to one's personal disposition towards God? Or is just an indication either of indoctrination or disordered appetite? Should we perhaps be wary of turning discussion of the natural law into a liberal search for a public reason accessible to all? Is personal dignity offended when people are "coerced" into accepting valid laws with which they disagree?
