King's generation also had much thicker skin than its descendants do. However, you are ignoring the fact that in King's time, black economic progress grew in leaps and bounds never seen before or since. It was the progress, not the injustices, that inflamed King & Co. Were injustice a motive for action, blacks would have acted most aggressively during slavery, somewhat less during Jim Crow, and not at all (or barely) by the 1960s.
So, maybe, just maybe, you are looking at King's generation through pc blinders.