The opening of "I have a Dream" is effective in that it (1) demarcates its own historical significance right at the start ("go down in history as the greatest demonstration for freedom in the history of our nation"); (2) it hits a persuasive emotional note early on ("momentous decree came as a great beacon light of hope to millions of Negro slaves who had been seared in the flames"); (3) it presents the problem immediately afterward ("But one hundred years later, the Negro still is not free. One hundred years later, the life of the Negro is still sadly crippled by the manacles of segregation"). These points do make the opening of this speech effective regardless of one's opinion on the problem because these three aspects of the speech do trigger interest--either positive or negative--in what King is about to say and in whether he can prove his assertions and--more importantly--in whether he can and will present a solution or a path to follow to arrive at a solution to the problem asserted.
Let me add this little tidbit passed on to my by a professor in one of my graduate classes. This speech, as remarkable as it was, was not scheduled for that day, so one has to wonder if it was off the cuff or prepared. The story as the professor relates it was that King was exhausted after the packed schedule for the events at the time. Noticing that he was losing some energy, Mahalia Jackson, who shared the platform with King, leaned forward and said, "Tell them about the dream Martin."
I agree with other posters. This is a classic speech that can be studied for its persuasive techniques. What is remarkable about it is the way that it balances emotion and reason through its appeal and captures the imagination of its audience through the vision of the future that King lays out. Yes, it may not convert people opposed to King and what he stands for, but it remains an incredibly powerful example of a speech that enflamed public consciousness.
This depends to some extent on the attitude that you have as you read or listen to the speech. King's speech is really intended as a way of "preaching to the choir," not as a speech that will persuade anyone who is against King's point of view. Since we, today, all agree with King, we think that the opening is effective. If we did not already agree with King, however, the opening would be much less effective.
As a speech teacher, I must agree with your first poster, that the "I have a Dream" speech is not only effective, it is a classic example of persuasive speech format.
Under Monroe's Motivated Sequence (which is the persuasive speech format I teach), the first part of a persuasive speech should always include a "Hey" or "Hey, pay attention" (an attention-getting device).
What better way to get an audience's attention, then by basically telling America that it welshed on a promise to the blacks. That a promise made by our forefathers was not kept. Anytime you start a speech with a startling statement, or a description of a big conflict or problem...you've captured the attention of most of those listening.
Let's say you were an American in 1963 who thought great strides had been made in the civil rights movement, and then Dr. King says the following near the beginning of his speech:
But one hundred years later, we must face the tragic fact that the Negro is still not free. One hundred years later, the life of the Negro is still sadly crippled by the manacles of segregation and the chains of discrimination. One hundred years later, the Negro lives on a lonely island of poverty in the midst of a vast ocean of material prosperity. One hundred years later, the Negro is still languishing in the corners of American society and finds himself an exile in his own land. So we have come here today to dramatize an appalling condition.
That statement would certainly make me rethink my position...and so it did for many in the crowd that day.
Indeed they are. That Dr. King stood before the Lincoln monument created the perfect setting for the Civil Rights speech as it evoked the history of the emancipation of Negroes after the Civil War. Now, a new emancipation was demanded: an emancipation from Jim Crow Laws in the South and racial discrimination throughout the United States.
King's effective use of metaphor and repetition lend a stunning impact upon his listeners. Likening the promise of freedom given in the Emancipation Proclamation to a defaulted promissory note and alluded to the words of the Declaration of Independence, King arouses the sense of injustice in the government's failure to truly free the blacks:
"It is obvious today that America has defaulted on this promissory note insofar as her citizens of color are concerned. Instead of honoring this sacred obligation, America has given the Negro people a bad check, a check which has come back marked 'insufficient funds.'"
Declaring that he is happy to join the thousands of other in "what will go down in history as the greatest demonstration for freedom," King immediately places tremendous importance upon the occasion. These words catch the attention of any reporter present. Then, King's use of Lincoln's words from the speech at Gettysburg, "Five score years ago," certainly ties this moment to the historically important time of Lincoln and the freeing of slaves. Thus, the impact of King's speech is great.