Emotion is the driving force behind all our actions. When we're happy, we tend to do things that we enjoy to express our happiness. When we're sad, we'll mope around, not talk as much, probably not do anything productive. When we're angry, we tend to act irrational and harsh, and do things we probably would not mean to.
Emotion has the immense power to create new things; however, it can also destroy. Emotion can't be described as good. It can't be described as evil, either. The only person who can control how you feel is you. And since only you can control how you feel, you have the power to determine whether to use your emotions for good deeds or for evil actions.