That’s a question that is so important to know the answer to, and there are competing theories.
What did Martin Luther King, Jr. think about it? Well, he agreed with St. Thomas Aquinas and quoted that great saint and philosopher when speaking about laws:
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.
From veteran journalist Sheila Liaugminas’ blog.
I’ve been having conversations with my coworkers about this very topic, and we do not all agree on this, so all the better to have wise, faithful men like Martin Luther King, Jr., and St. Thomas Aquinas on your side!

Very good post. Even these many years later, King is still a controversial figure among some in my little corner of the deep south. Our town started a Martin Luther King parade about 10 years or so ago. Part of the parade route goes right by my house. Our neighborhood is mostly older homes and mostly white folks. The first couple of years of the parade, my wife and my kids and I were the only neighbors seen out watching the parade. When we had the parade the other day, about half the neighbors sat out in their yards to watch. I know that’s small progress, but at least it’s something.
I’ve often thought that we in the south were so fortunate that King and the other leaders of the civil rights movement were committed to the principles of non-violence. The violence that did occur was bad enough, but it would have been exponentially worse had non-violence not been taught and stressed by King and other leaders. One need only look around the world to see examples of how it could have been much worse. Think how much better off the Palestinians would be today if they were led by people like King instead of Arafat and now Hamas.
Martin Luther King had a ton of personal flaws, but he left the world a much better place and we should all be so fortunate to say so at the end of our lives.