The whole essay is worth a read and it’s quite short.

Another choice quote to BTFO radical centrists from this letter is:

You deplore the demonstrations taking place in Birmingham. But your statement, I am sorry to say, fails to express a similar concern for the conditions that brought about the demonstrations. I am sure that none of you would want to rest content with the superficial kind of social analysis that deals merely with effects and does not grapple with underlying causes. It is unfortunate that demonstrations are taking place in Birmingham, but it is even more unfortunate that the city’s white power structure left the N*gro community with no alternative.

Which echoes his famous “a riot is the language of the unheard” speech - The Other America.