Warning: incredibly nerdy Star Wars fanboy explanation incoming
The Force has no dark side or light side. If it is, as the films would have us believe, a natural force (although I don't buy into that whole midichlorians B.S.), then why would it be good or evil? The Force itself is neutral; people can be considered light or dark, but that's a reflection of the person, not the Force abilities they use.
Powers are not good or evil: it depends entirely on how you use them. A Jedi could use Lightning to kill a Sith, and that would be considered good; likewise, a Sith could use Heal on his apprentice, and that would probably be considered evil. To sum up: the Force is neutral. Your side depends on you, and how you use the Force.