Yes, Martin Luther King signed the letter to Paul VI asking him to reconsider Humanae Vitae. But so did the future Father Ricard John Neuhaus. And, as Ronald J. Rychlak writes:
On April 12,1963 -- Good Friday -- Rev. Martin Luther King Jr. led a group of about 50 anti-segregation protesters into downtown Birmingham, Alabama. It was a peaceful protest, but they were not naïve: They knew that their message would offend and cause problems. King was not surprised when they were all arrested.
Eight white clergymen from Birmingham, including a Catholic bishop and a rabbi, wrote a letter appealing to the black population to stop such demonstrations. These clergymen were not bigots; they just did not want the kind of confrontations that King had provoked. They wanted to let the courts work toward integration. Their letter was published in the local newspaper under the title, "A Call for Unity."
King's response to the clergymen, his "Letter from a Birmingham Jail," was one of the finest modern appeals to natural law. In it, he wrote: "I would agree with St. Augustine that, an unjust law is no law at all." Moreover, "Injustice anywhere is a threat to justice everywhere." As such, "One has . . . a moral responsibility to disobey unjust laws."
King's analysis, of course, raises the question of how to determine whether a law is just. Here, King turned to natural law. He explained: "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." He then looked to St. Thomas Aquinas: "An unjust law is a human law that is not rooted in eternal law and natural law." Applying that to the case at hand, King explained: "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."
Directly responding to the clergymen, King wrote: "In your statement you assert that our actions, even though peaceful, must be condemned because they precipitate violence. But is this a logical assertion?" After providing some examples, he explained his problem with the suggestion that they should wait for the courts to act: "It is wrong to urge an individual to cease his efforts to gain his basic constitutional rights because the quest may precipitate violence. Society must protect the robbed and punish the robber."
King explained that "oppressed people cannot remain oppressed forever. The yearning for freedom eventually manifests itself, and that is what has happened to the American Negro. Something within has reminded him of his birthright of freedom, and something without has reminded him that it can be gained."
King said that a change had come in his way of thinking: "I have tried [in the past] to make clear that it is wrong to use immoral means to attain moral ends. But now I must affirm that it is just as wrong, or perhaps even more so, to use moral means to preserve immoral ends." Thus, the legal system, while "moral" in and of itself, was at that time in history protecting the immoral system of segregation. At the very least, it was moving too slowly to satisfy the yearning for freedom. As King explained: "Past promises have been broken by the politicians and merchants of Birmingham and now is the time to fulfill the natural right of all people to be treated equal."
King expressed frustration with the inability of many church leaders to grasp these truths while they were hiding behind the "anesthetizing security of stained-glass windows." Even in his frustration, however, he expressed his love: "In deep disappointment I have wept over the laxity of the church. There can be no deep disappointment where there is not deep love."
King's letter certainly struck a chord. Some have called it the turning point of the civil rights movement. It seems also to have had an impact on the Catholic bishop who signed the letter to which King responded. That bishop, Joseph Aloysius Durick, ultimately became known as a strong voice for civil rights. Over local opposition, he put in place the decrees of Vatican II that were intended to eliminate racial divisions and show compassion for the poor and socially marginalized.
These actions drew national attention. Bisohp Durick was sometimes boycotted when he made personal appearances, but with support from Pope Paul VI and the truth of natural law, he stood firm and reshaped the hearts of many Catholics in the Deep South. Of course, Martin Luther King Jr., writing from a jail cell in Birmingham, Alabama, played a huge role in that process.