What does King feel that many African Americans will do if white Southerners resist his non-violent approach?

Excerpt from Letter from a Birmingham Jail, by Dr. Martin Luther King Jr., on April 16, 1963Perhaps it is easy for those who have never felt the stinging darts of segregation to say, ‘Wait’. But when you have seen vicious mobs lynch your mothers and fathers at whim; when you have seen hate filled policemen curse, kick, brutalize and even kill your black brothers and sisters;... when you see the vast majority of your twenty million Negro brothers smothering in the air-tight cage of poverty; ... when you have to concoct an answer for a five-year-old son asking:... ‘Daddy, why do white people treat colored people so mean?’...then you will understand why we find it difficult to wait. You speak of our activity in Birmingham as extreme. At first I was rather disappointed that fellow clergymen would see my nonviolent efforts as those of an extremist. I began thinking about the fact that I stand in the middle of two opposing forces in the Negro community. One is a force of complacency, made up in part of Negroes who, as a result of long years of oppression, are so drained of self-respect and a sense of "somebodiness" that they have adjusted to segregation; and in part of a few middle-class Negroes who, because of a degree of academic and economic security and because in some ways they profit by segregation, have become insensitive to the problems of the masses. The other force is one of bitterness and hatred, and it comes perilously close to advocating violence. It is expressed in the various black nationalist groups that are springing up across the nation, the largest and best known being Elijah Muhammad's Muslim movement. Nourished by the Negro's frustration over the continued existence of racial discrimination, this movement is made up of people who have lost faith in America, who have absolutely repudiated Christianity, and who have concluded that thewhite man is an incorrigible "devil." I have tried to stand between these two forces, saying that we need emulate neither the "do nothingism" of the complacent nor the hatred and despair of the black nationalist. For there is the more excellent way of love and nonviolent protest. I am grateful to God that, through the influence of the Negro church, the way of nonviolence became an integral part of our struggle. If this philosophy had not emerged, by now many streets of the South would, I am convinced, be flowing with blood. And I am further convinced that if our white brothers dismiss as "rabble rousers" and "outside agitators" those of us who employ nonviolent direct action, and if they refuse to support our nonviolent efforts, millions of Negroes will, out of frustration and despair, seek solace and security in black nationalist ideologies--a development that would inevitably lead to a frightening racial nightmare.