King, particularly in his last year, was a challenge and, to some, a threat to the arrogance of American Exceptionalism and its accompanying and growing militarism.
That is to say he was beginning to speak to America's bad conscience, warning the Lady of Light and Liberty that she was in danger of becoming Madam in a Fat Car, Bitch of Babylon.
Everyone has heard and remembers, "I have a dream...".
But how many have ever heard, let alone remember, "The choice is not between violence and nonviolence, the choice is between nonviolence and nonexistence."?
I've thought and written about this phenomenon before and I wish I could coin a term for it:
When prophets cannot be silenced, when they are dead, as much truth is drained off as can be gotten away with without making them look completely bloodless.
What remains is diluted with trivialities.
Then they are sealed in plastic, placed on a pedestal and, if needed, their birthday becomes a national holiday.