The list of questions that follow the main question in Langston Hughes' short poem "Harlem" may serve to make us, as the readers, think about the full range of possible reactions to the situation in the initial question: "What happens to a dream deferred?" To me, the poem (or poet) never clearly points to one possible reaction as the most likely one, but the sixth and final possibility -- "Or does it explode?" -- is given particular emphasis. It's set apart in a stanza of its own, it's shorter than most of the other questions, and it's the final question, the last possibility that we're left with.
That final line to me has always seemed to hint at possible violence that may result when people (African Americans, to be more specific) aren't given full citizenship and genuinely equal opportunities in the United States. The desperation and rage that have fueled a number of race-riots, for example, seem to be predicted in this final line of the poem.
See the links below for the study guide to this poem and for a similar discussion from just a month or so ago.