In these lines, Martin Luther King makes an allusion to Socrates, one of the most important philosophers of Ancient Greece. Socrates is a very admired figure in the West, and most people believe him to have been intelligent and just. Therefore, by making an allusion to this character, King wants to increase the credibility of his actions. He wants readers to intellectually agree to the quality of King's argument, and in this way, be supportive of his course of action.
Dr. Martin Luther King shows his democratic principles in this exerpt in his use of the words "rise from the bondage of myths and half truths' as well as 'the need to 'help men rise from the dark depths of prejudice' through nonviolence.
What supports his cred well he has a first hand experience, of the white apprehension in south Africa, Yeah its extremely justified because the people of color of south Africa had been through a lot. PS this answer isn't so great