I think the series's position on evil is strong but instinctual: it knows evil when it sees it. Eventually patterns appear. Only many readers also see other patterns different from the ones the ones the author's.

Harry, Ron and Hermione and their friends are good and fight evil as personified by Voldemort and other people who strongly oppose them. LV's brand of bigotry (saying "Mudblood" and other Nazi parallels, etc.) is evil. You need courage to fight evil--cowardice is possibly the root of most if not all evil in this universe, so giving in too much to cowardice is dangerous. Certain kinds of love are good. It feels like the author is emotionally sure of good/evil when she's writing and that comes through in scenes, but there's no deep, coherent philosophy about it worked out--sometimes it's conflicted.