What's a modern day application of this principle? The best example is efforts to redefine marriage and force members of society to affirm and support homosexual marriage. Why? Because homosexual marriage directly violates God's law or the moral law as stated by King.
... One may well ask: "How can you advocate breaking some laws and obeying others?" The answer lies in the fact that there are two types of laws: just and unjust. I would be the first to advocate obeying just laws. One has not only a legal but a moral responsibility to obey just laws. Conversely, one has a moral responsibility to disobey unjust laws. I would agree with St. Augustine that "an unjust law is no law at all."
Now, what is the difference between the two? How does one determine whether a law is just or unjust? 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. 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. Paul Tillich has said that sin is separation. Is not segregation an existential expression of man's tragic separation, his awful estrangement, his terrible sinfulness? Thus it is that I can urge men to obey the 1954 decision of the Supreme Court, for it is morally right; and I can urge them to disobey segregation ordinances, for they are morally wrong.
Such a comment will no doubt infuriate gay activists. But one has to ask what is the basis for homosexual marriage except as a creation of man. I'm waiting for logic and sound reasoning which goes beyond statements like "justice requires it", "fairness demands it", "it's a basic human right that two men and two women be able to marry" and explains the basis for such assertions of justice, fairness and human rights. If one believes society's ultimately decide what's just, fair and a basic human right then we're left with no basis to argue against Hitler's Nazi Germany, because that's what that society decided at that time.