To answer this you must first understand Harry's world which Rowling has constructed. It is a world where good and evil battle for dominance. After reading the first four books there is no clear evidence that good or evil will prevail. Harry seems to be the best hope the good side has to offer. This uncertain balance between good and evil is called dualism.
Dualism is the dominant theme of eastern thought and philosophy.
Both good and evil are necessary to maintain the balance of life. If one side were to get the upper hand the balance of life would be disturbed. In the world of the dualist, both good and evil are needed. This is distinctly different from the Biblical worldview, which teaches us that not only will evil be defeated, but that God through His Son, Jesus Christ, has already won the victory. The presence of evil is not ultimately necessary to maintain balance and perspective.