Someone recently asked (in a Yahoo group), "Why is Dark synomous with Evil?"
And I replied:
Because humans don't see very well in the dark.
And, because lots of animals that are very dangerous to humans see very well in the dark.
We evolved in a world that wasn't so safe and nurturing in the daytime, so when the lights went out people naturally huddled close together, generally mindful if not scared out of their wits, that dangerous, evil, things lurked just outside their campfire (assuming they had one).
Later, that mindset extended to more organized humans, collected in towns and cities. The latter could usually afford to build a wall, a perimeter against nasty evil nature, which was always threatening anyone who ventured out into it, especially at night.
However, paradoxically, humans have always reacted against this walling-off, and Greeks for example, expected their young people to be initiated into the dangerous but knowledgeable (Knowledge being understood as double-edged) world of adulthood by being taken beyond the threshold of civilized existence back into the natural world outside the wall. If they survived (most of the initiations were not as rigorous as things Spartans put their boys through), they would be made stronger and wiser for it.
Pan is a god of the threatening, but initiatory, dark side. He can scare the devil out of people, literally panic them; but he can also give them opportunities to develop the strength to stand up to what they fear, using their human intelligence to learn not to be afraid of the shadows.
Still, once must respect the shadows for the dangers that still lurk there. Nobody wants to have his life's lesson be one that has no second chance. Unfortunately, in real life, there are many kinds of instruction that will teach others about our mistakes, but kill us as the example.
When you think about it, the ability to walk comfortably in the dark, to even love doing so, is also a willingness and love of the light as well. For they are sides of the same living experience.
As occultists have said, and I have said (recently), Death is required for Life. And Dark for the Light.