Kaiyanwang
Adventurer
Evil is not an element, as in fire or water, but is physical in D&D. Sartre lived in the real world which is not a "black and white" universe like the D&D one - for the record, it goes without saying, but I am in no way, shape and form advocating this point of view for this universe.What does that even mean? Evil is not a substance. Evil is a subjective concept; it's a term that only has meaning when given context. You can't be made of evil. That's like being made of red, or made of comfort, etc..
You can say the words "a plane of pure evil," for example, but those words will mean something different to every single person. Some might picture something like their interpretation of a stereotypical Christian conception of Hell. Others might imagine a void. According to Sartre, Hell is other people.
That's why Gary Gygax can describe Lawful Good by using examples that sound plenty evil from my perspective.
See my early post for details.