Indeed, I've often been upset by settings that DO have absolute good and evil. It weakens story telling possibilities. And frankly, it makes no sense.
I'm not fond of black and white settings, and indeed, D&D doesn't allow for that - that's why we have the Neutral alignments.
But when Evil and Good are forces, it doesn't make sense to say "Oh yeah, using evil energy isn't evil."
It might not be evil the first time, but evil energy is, since it's EVIL, corruptive. And as such, will corrupt the user over time.
Alignment shifts exist for a reason ya know.
It's not like D&D/Pathfinder doesn't HAVE moral ambiguity - hell, even necromancy, despite having the [evil] tag on all of the cool spells, has some moral ambiguity because it deals with negative energy, not evil energy. Yeah, there's a difference.
This is the same game that makes a distinction between light and holy.
But making EVERYTHING morally ambiguous is... well, honestly, it's even more cliche than making everything black and white anymore.
It's a fantasy game. I don't want it to be like the real world. Not everything needs to be deep.