Suppose it is said that there are evil spirits: — if they have their power from the Gods, they cannot be evil; if from elsewhere, the Gods do not make all things. If they do not make all things, then either they wish to or cannot, or they can and do not wish; neither of which is consistent with the idea of god. We may see, therefore, from these arguments, that there is no positive evil in the world.
It is in the activities of men that the evils appear, and that not of all men nor always.

XII. The origin of evil things; and that there is no positive evil. - On the Gods and the Cosmos