At the end they try to explain to Robin their concept of good vs evil, or "good deeds causing evil vs evil deeds causing good", and that works for me.
The problem is that the story doesn't actually work on its own metaphysical level. Yes, everyone sees themselves as the heroes of their own story, and yes there are times when good intentions lead to bad outcomes and vice versa, but that doesn't really change the fact that in the real world, "good" and "evil" are abstractions of intention and desire, with "good" generally correlating to altruistic and/or beneficial acts and "evil" correlating with selfishness, broadly speaking. In this world, somehow "good" and "evil" exist as actual alternate dimensions and power sources for magic, but their effects don't actually correlate to "good" and "evil" as someone might actually use the words to describe anything. No matter what your opinion of brainwashing and "light-minding" in the book, rape is pretty much godawful and evil; how can Mizzamir be the leader of "good" and, in fact, be accepted by the dimension of pure "good" as its avatar when he is an unrepentant rapist?
Ergo, they've just got a dimension of heat and light and a dimension of entropy and shadow from which they draw magical power, and I'm happier with the story when I mentally replace every reference to "good" and "evil" with "Plains" and "Swamps" respectively.