Consider the following comment about Kurt Vonnegut: "Vonnegut has said that his purpose as a writer is to get people before they become generals and presidents and 'poison their minds with humanity.'" Does this comment give you insight into Vonnegut's purpose in Harrison Bergeron? What does the story say about "humanity"?
That Harrison wants to establish himself as emperor indicates that he, too, knows only conformity and control. So, he has lost his sense of humanity, as well, and gone too far. Like those in conformity, he seeks only comfort and security--just on a different level.
By choosing the word "humanity" and giving it a negative connotation, Vonnegut shows his belief that mankind's nature is to control others and to try to force conformity upon others. Vonnegut suggests in most of his short stories that government and other leaders in society use conformity to establish totalitarianism.
In "Harrison Bergeron" specifically, Vonnegut uses Harrison's character to show that he has not yet been "poisoned." This is why it is significant that Harrison is young. In general, the story argues that humans have an innate desire to be individuals (this is why the HG must make everybody equal and remove any way that someone might stand out from the crowd). The story also portrays most of humanity as being afraid to not conform (notice how Harrison's parents give him up to the Handicapper Generals' men).
What an interesting quote about poisoning the minds of future politicians! I definitely think this relates to his purpose in writing "Harrison Bergeron" which is at its heart a story about the problems of authority and ways people will keep power. I would definitely discuss the concepts auntlori referred to and include some specifics about Hazel and George's handicaps and their inability to feel sadness for their son's death because of the handicaps placed on them. The compassion that Vonnegut tries to elicit from the reader is clearly devoid from the Diana Moon Glampers - The Handicapper General.
Vonnegut clearly believed those in authority are careless and even harsh regarding the well-being of their fellow men (and women, of course). This quote suggests his hope was to forestall such potential oppression by instilling an awareness and appreciation for the value of all persons so that the next generation of leaders would conduct business with compassion and understanding rather than hatred and cruelty.
Much of what I've read of Vonnegut's makes me think of that idea of trying to teach people to be people before they get too powerful to remember that. In thinking of Harrison Bergeron in particular, the way that Vonnegut portrays the people and the way they have been brought down to try and equalize them helps to remind the reader that people aren't equal in ability or appearance, etc., and that trying to make them equal isn't really helping anything.