There are several possible themes in "Harrison Bergeron" by Kurt Vonnegut, but the one that stands out is that complete equality is dangerous. In Harrison's world, the people are forced to give up their individuality in order to have a peaceful, conflict-free society. Competition has been completely quashed by the government, and "just average" is valued so much that a Handicapper General has been appointed to make sure no one is better than anyone else. She does this by requiring beautiful people to wear hideous masks and by making athletic people wear heavy bags to weigh them down, etc. This is dangerous because people have no reason to be their best anymore-"best" is looked at disdainfully. If our society did not value intelligence, talent, and/or athleticism, think of how demeaning that would be to individuals and think about how different our world would be!
"Harrison Bergeron" is still relevant today as a cautionary tale. Most of us believe that equality is important and necessary in our society, and we are willing to give up some of our freedoms in order to keep our citizens safe. For example, after 911, we quickly got used to, and accepted, more stringent checks at airports. On the other hand, we might not so quickly be willing to have government officials show up at our front doors to check on our recent activities. We need government to govern fairly, but we don't want our individuality taken away in the process. We realize that competition is healthy because it can make us all try harder and be better people.