Much of the news grabbing reactions extolling the actions of Kim Davis is prefaced by a direct quote from Dr. Martin Luther King's Letter from a Birmingham Jail in which he explains the difference between just and unjust laws. In his letter he states, quite directly that 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."
Of course to stop with the 'headline,' as many commentators seem to do, allows a simple acceptance of a single interpretation of what King meant by "God's Law" that can end up being a misinterpretation,
Good writers understand that it is the clarification of abstractions that matter, and good readers often hang around for the deeper explanation. This is a part of the actual interpretation that King wrote that follows the above referenced quote. I suggest that anyone, who after reading, this who thinks Reverend King would support Kim Davis' discrimination against Gay persons seeking to legally marry should take some reading lessons and read it again.
"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. 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. Any law that uplifts human personality is just. Any law that degrades human personality is unjust. All segregation statutes are unjust because segregation distorts the soul and damages the personality. It gives the segregator a false sense of superiority and the segregated a false sense of inferiority. Segregation, to use the terminology of the Jewish philosopher Martin Buber, substitutes an "I it" relationship for an "I thou" relationship and ends up relegating persons to the status of things. Hence segregation is not only politically, economically and sociologically unsound, it is morally wrong and sinful."
The complete text can be read here: Letter From a Birmingham Jail