Answer:
The practice of the Craft, is not divided into good/bad, white/black, light/dark or any other polarities.
Like all spiritual paths, Paganism/Wicca is practiced by humans, and humans are very complex creatures, who never (I repeat never) are completely one thing.
The energies and powers used in the Craft exist, with or without being noticed, tapped into, channeled, or used. Those powers do not have a polarity any more than electricity running through a line has polarity.
Pagans (Wiccans included) make every effort to be as good as they can be, some are less good at it than others, but that can be said of lawyers, priests, school teachers, police officers, and very nearly everyone else in the world.
You judge others by their actions, but I have never heard anyone ask if someone was a dark or light human.