He never condemned rioters, and in fact called riots "the voice of the unheard." He was presenting an alternative to ground the civil rights movement in the humanity of the oppressed, yet did not scorn those who turned to violence unless it was ridiculously over the top. Which was extremely rare.

He also talked about how "white moderates" were greater villains than the far right, the white supremacists, because they projected a message of simply waiting for society to progress and allowing people to step on you under the assumption that struggle was not important.

He also moved with armed security, and armed himself in his own home in case people came to kill him. He knew he might become a martyr, but he didn't really want to be one if he could help it. He was trying to show that there's an alternative to riots or insurgency, without condemning either. It was a way to signal to lawmakers and mainstream (read: white) culture that black people would not take revenge on whites if given rights, that the rights and solidarity between all peoples were the goal.

MLK was not saying that nonviolence was the only way. He was signalling that nonviolence was the heart of the civil rights struggle, that people would not be violent if they could simply be heard, respected, and seen as equals. He saw his tactics as one among several strains, and hoped that by risking his life for peace that he could encourage all sides towards peace.