Randy Barnett, of the Volokh Conspiracy, has a lengthy post describing his approach to defining the legitimacy of a legal system. He is drawing on concepts that he outlines in his book, Restoring the Lost Constitution (which is on my ever-growing list of books to read). Here are some selections from his 8-point discussion that I found interesting:
(1) The concept of "legitimacy" I am considering concerns whether laws that are imposed on the people create a prima facie (i.e. rebuttable) duty of obedience because they are laws, or (another formulation) are presumptively binding on conscience.These two points are related in that if an obligation is objective it is necessarily binding on the conscience. What he means by rebuttable or presumptive is that if a law is passed through legitimate means it is presumed to be a legitimate (ie binding) law unless it is shown not to be on substantive grounds. In the latter case, it can be repealed through the same procedural methods. I metion this because there are some who confuse legality with morality, but that isn't what Barnett is talking about here.
(2) The concept I am considering is objective, not subjective. By this I mean that I am not discussing the perception that there is a prima facie duty to obey the law, but whether any such perception is valid or justified.
One route to legitimacy is the consent of the governed, but [...] the consent of some can never explain how nonconsenting persons come to be bound in conscience. This is the challenge to constitutional legitimacy made famous by Lysander Spooner [...] I try to meet Spooner's challenge by positing an alternative route to legitimacy. (a) No one can complain about the imposition of a law if it does not violate his natural (prepolitical) rights; (b) because one has a duty to respect the rights of others, one also has a duty to obey a law that is necessary to defining and protecting the rights of others. A coercive command that meets these two requirements is "just" and binding in conscience. Therefore (c) a law is legitimate (in the sense defined above) if it is produced and enforced by procedures that make it more likely than not that it (a) respects the rights of the persons on whom it is being imposed and (b) is needed to protect the rights of others. In this sense "constitutional legitimacy" is procedural in nature, though the procedures must be assessed with a background theory of substantive rights in mind.This is a very powerful concept and bears re-reading. From a Christian point of view, this account of legitimacy allows reconciliation of the often thorny choice between being submissive to the established authorities (Rom 13: 1-7) and obeying God rather than man (Acts 4:19). If, as I believe, establishing justice in the land (1 Cor 6:2) is a duty of the Christian in a democratic society (ie a land in which every man is king) then this notion of legitimacy allows us to participate in a society where the substance of the laws is ungodly, provided there is a legitimate (in the above sense) system whereby laws can be changed. So long as there is hope that the ungodly laws can be changed, we are not obligated to break the law, for instance, by destroying abortion clinics or freeing slaves. However, a corollary is that if it ever becomes clear that there is no legitimate process by which laws can be changed, (such as is the case for Christians in Sudan, for instance), rebellion is justified.