Commentary: We honor King as a national hero. But movements for racial justice still get labeled unpatriotic.

Because Martin Luther King Jr. now stands as an exalted hero of American history, we tend to assume that his assassination 50 years ago was experienced as a national tragedy. Yet in the days and weeks after his death on April 4, 1968, Americans not only mourned and grieved but also seethed and raged. President Johnson…