Originally Posted by
gloryblaze
I think the issue here is that the ultimate question ("What ought one do?") in the moral theory proposed by OldTrees (and which seems to be a real philosophy, based on his descriptions) is asked in a vacuum, not from the perspective of any person.
You said that the drow priestess's ideals align with the in-universe alignment "Evil". This can be true. You then said she "ought to live by that alignment." And from her perspective, this is true and she will do so.
The issue is that the question "what ought one do?" in OldTrees's moral theory is not asked from her perspective. It is asked in a vacuum, in a white room. In an RPG, it is defined by the GM. So if the GM decides that it is "moral" to follow the in-universe alignment "Good", then the drow priestess is objectively wrong to follow the in-universe alignment "Evil", even though doing so is what she believes she ought to do based on her ideals. Her ideals themselves are objectively wrong under this moral theory. She is mistaken that one ought to be Evil.