I came to this thread again, thinking I might have something new to give to the discussion.
Then I re-read the first page and realize that No-Name already brought the question out. lol
Thoughts on evil:
Growing up, I often heard tv shows and religious fundamentalists talk about evil as though it were a tangible thing, with clearly defined parameters. Ideas like "evil by nature", or "pure concentrated evil"

etc. struck me as bizarre.
I mean, in the christian mythology, aren't demons really just angels who developed a problem with their authorities? Christ, I've a major problem with authority. Does that make me "evil"?
To me, I figure the baseline for evil is the willful failure to consider the other guy's situation.
Under this I'd add; knowingly causing needless cruelty, and all forms of physical/psychological damage or distress. Basically, don't hurt anyone if you can avoid it.
Examples: * Outrageous Greed hurts people, just in an indirect way.
* Forcing someone into doing something they feel is wrong, is a way of hurting them.
All the rest is just cultural/religious artistic license.
But for the point of EC stories and such, the idea of evil having a substance, and the idea that the universe runs on a moral framework makes it work better.
I mean such ideas like the one saying that if someone commits one sin, it leaves a door of sorts open for Evil to take them. These make for good story material in this genre.
All the demon has to do is to guide the girl to do one thing she feels is 'sinful', then the demon can take her and the transformation begins.
Thoughts?
Also, outside of tf material, any thoughts as to why demons are so often shown looking monstrous and bestial? It's an insult to beasts that our personification of all our worst qualities look bestial.
We're far worse than anything with claws or fangs, wouldn't ya say?