There is a very insightful and provocative post by HamdenRice on Dailykos.com. This is a central argument in there:
But what most people who reference Dr. King seem not to know is how Dr. King actually changed the subjective experience of life in the United States for African Americans. And yeah, I said for African Americans, not for Americans, because his main impact was his effect on the lives of African Americans, not on Americans in general. His main impact was not to make white people nicer or fairer. That’s why some of us who are African Americans get a bit possessive about his legacy. Dr. Martin Luther King’s legacy, despite what our civil religion tells us, is not color blind. . . . I would like to remind everyone exactly what Martin Luther King did, and it wasn’t that he “marched” or gave a great speech. My father told me with a sort of cold fury, “Dr. King ended the terror of living in the south.” Please let this sink in and and take my word and the word of my late father on this.
The evidence for this impact of Dr. King and many other African Americans who fought a real system of totalitarianism and terror, especially but not exclusively in the Jim Crow south, can be found in much research literature and popular accounts, for example here. But somehow has not made it into the mostly white-controlled media or educational curricula.