Without evil there is no good, without a villain there is no hero. Since a young age, we have been taught that we cheer on the hero and hate the "bad guy. There are villains in movies and in books because we need someone or something root against or to fail in their ventures. In every story there has to be an antagonist, an enemy of the hero. Most of the time we know immediately who the villain is, he's the "scary guy, maybe wearing a mask, dark clothing, or just seems sinister and mysterious. There are many villains in movies, books, and even real life, but before declaring who the villain is, it must first be decided what a villain is and why we have them and create them.
There are many different reasons to have villains, the first being that it would seem extremely odd in a world without them. Villains have been around since the creation of the world, all the way back to biblical times. If there were not any villains we would have superheroes flying around in funny costumes with their underwear on the outside of their clothes for no apparent reason. There would be no purpose for police officers, firefighters, or the judicial system at all. And if there are no bad guys, just who are the good guy