It would take a special sort of "chutzpah" to say that someone who spent over a decade in danger being threatened, beaten, arrested, stabbed, shot at, spied upon, and assaulted without lifting a finger in retaliation all before he was finally murdered didn't really believe what he preached.

Whenever the issue of compensatory treatment for the Negro is raised, some of our friends recoil in horror. The Negro should be granted equality, they agree; but he should ask nothing more. On the surface, this appears reasonable, but it is not realistic.
-From "Why We Can't Wait".


Now there's another myth that I want to mention, because if we are going to have action programs that will prod the forces in power so that they will make the necessary concessions, we are going to have to understand why the forces in power need to be prodded. Now this leads me to say that we've got to get rid of the myth of over-exaggerating the bootstrap philosophy. I guess that it is all right to tell a man to lift himself by his own bootstraps, but it is a cruel jest to say to a bootless man that he ought to lift himself by his own bootstraps. Through centuries of denial, centuries of neglect, and centuries of injustice many, many Negroes have been left bootless. This does not mean that we do nothing for ourselves. It does not mean that we should not amass our economic and political resources to reach our legitimate goals. It simply means recognizing, the nation recognizing, that it owes a great debt on the basis of the injustices of the past.
-1968 Speech to Ohio Northern University


Within common law, we have ample precedents for special compensatory programs, which are regarded as settlements. American Indians are still being paid for land in a settlement manner. Is not two centuries of labor, which helped to build this country, as real a commodity? Many other easily applicable precedents are readily at hand: our child labor laws, social security, unemployment compensation, man-power retraining programs. And you will remember that America adopted a policy of special treatment for her millions of veterans after the War—a program which cost far more than a policy of preferential treatment to rehabilitate the traditionally disadvantaged Negro would cost today.

The closest analogy is the GI Bill of Rights. Negro rehabilitation in America would require approximately the same breadth of program—which would not place an undue burden on our economy. Just as was the case with the returning soldier, such a bill for the disadvantaged and impoverished could enable them to buy homes without cash, at lower and easier repayment terms.
-1965 Playboy Interview

There's much more of course but the point is made. MLK not only believed in affirmative action but practiced it via Operation Breadbasket which identified and pressured companies that did not hire black people. It's really important that people know the history.