What does King mean by “constructive nonviolent tension” and how does he define his goal?

Acknowledging that words like “tension” and “crisis” are frightening to moderates, Dr. King nevertheless insists that he embraces such concepts, provided they are “constructive [and] nonviolent.” In fact, he believes that tension is necessary for growth. He alludes to Socrates, who believed there must a “tension in the mind” so that individuals could transcend superstition and embrace truth, and insists that men like himself must force external tension so that men can “rise from the dark depths of prejudice and racism to the majestic heights of understanding and brotherhood” (172).
Therefore, he absolutely agrees that “negotiation” and “dialogue” should be the end game, but believes that it will not happen without a “crisis-packed” scenario (172).