Such a "moral" system can exist in the setting, sure, with its cosmic forces and its assertions.
Just means that unfairness, injustice, and wrongness are built into that setting's cosmic structure. Forget gods not being above right and wrong... universes and realities aren't above right and wrong. There are reasons underlying right and wrong, and those reasons don't stop being reasons just because it's another "reality". I'm not going to further tank the thread by listing off specific ugly and inflammatory immoral acts, but those acts don't suddenly become moral just because it's in another universe.
Is the question in this thread the stated "Why is Necromancy evil but Conjuration is not?"... or is it actually "Why is Necromancy evil but Conjuration is not, in the default/implied D&D setting?"
If it's the former, I've given my answer a few times. If it's the later, I don't have an answer, because it's a meaningless distinction. Either way, maybe I should just try to walk away.