Why do people put other people down?

Right now, politicians are attacking other politicians for mistakes in their past or for not agreeing with them. Newspaper commentators call the other side names because they're the "victim" and everyone else is the "bigot" and "hate-monger." My own peers vote me down if my opinion is not the way the majority thinks. Why can't we live in peace and just "be ourselves"? If everything should be "fair" and "equal," then who is to say what is good and what is bad? Why are we contradicting ourselves? Do we truly practice what we preach? I think not!