Answer: To appeal to his critics’ intellect.
Explanation: 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.