Good or Evil is an artificial concept and is entirely subjective to the beholder.
The naaru are the pinnacle of "good" in the warcraft universe, yet could still be evil to us if they consider us too "chaotic" or "corrupted" or just a detriment to their plans for the universe.
Even Sargeras thinks what he is doing is good since he wants to make sure the universe doesn't fall to the void.
We don't even know what the void lords their motives are, but we can be certain that they don't do things cause "LoL evil"
In the end, the magic you use isn't based on what it is or what you do with it. Because from someones point of view you are evil, but from your own you will always be good.