Martin Luther King, whose birthday was celebrated as a national holiday on January 16, was not very popular with conservatives in the 1960s. His endorsement of civil disobedience seemed to many to border on lawlessness, he had some questionable associations, and toward the end of his life he even threw in his lot with critics of the Vietnam War.

Since that time, his stock has risen. In particular, conservatives have come to love King’s "I have a dream" speech, in which he famously proclaimed that he dreamed of a day in America when his children would be "judged by the content of their character and not the color of their skin." This line—and the sentiment it encapsulated—has become a favorite weapon of conservatives in their fight against racial preferences and for equality under the law. Liberals retort that King himself (in a fit of inconsistency, though they won’t say so) endorsed such "affirmative action" policies.

The attempt to make King a symbol in the battle over a color-blind America has obscured at least two other ways that King’s life and words actually bolster the conservative case—and in these instances, liberals have virtually no rejoinder.

First, King himself was not just a "civil rights leader," as it is often put. He was a Christian minister who found himself thrust into the role of a civil rights leader. He attended seminary, was ordained, had a congregation under his care, and did all of the other things a pastor does. He entered the political arena because he saw injustice and was determined to fight it. To put it another way, he mixed religion and politics, because he saw in the law of the time something his religious duty called on him to oppose. Furthermore, he rallied his followers with an explicitly religious message.

He consequently stands as a ringing rebuke to those today who argue that religion and politics should never mix, that moral or religious rhetoric or argumentation have no place in the world of politics, and that the clergy should retain a posture of absolute neutrality on all worldly matters. King recognized that some worldly matters demanded by their nature to be addressed in moral rather than pragmatic terms. The abolitionists had already demonstrated that, as had the New England clergy of the 1770s, but King alone is honored with a holiday and with the universal veneration of the left.

Of course, if King’s life proves that some political issues call for a religious response, it does not prove which issues do or under which circumstances. Virtually no one in America of the left or right believes that every issue should be made a crusade. Is abortion such an issue? Is the preservation of traditional marriage? There is still room for debate, but one thing can be said for certain: logically speaking, no one who praises King can condemn the conservative churches en masse because their foray into political questions is inherently illegitimate.

Second, the specific nature of King’s religious argument poses a serious difficulty for the left’s rhetorical assault on social conservatism. That assault is based on an explicit or implicit relativism which condemns conservatives for their "intolerant" belief that absolute standards of right and wrong exist and can be discerned through revelation or reason. Martin Luther King may have been many things, but he was not a relativist.

His argument in this respect is laid out well in his Letter from a Birmingham Jail. In the letter, King holds that "[T]here are two types of law: just and unjust… I would agree with St. Augustine that ’an unjust law is no law at all.’" In King’s view, just law must be obeyed, while unjust law must be resisted. How does one tell the difference between just and unjust law?

A just law is a man-made code that squares with the moral law or the law of God. An unjust law is a code that is out of harmony with the moral law. To put it in the terms of St. Thomas Aquinas: An unjust law is a human law that is not rooted in eternal law and natural law.… [S]egregation is not only politically, economically, and sociologically unsound, it is morally wrong and sinful.