these are three different approaches to the "moral universe" of the dungeon.
my failure to recognize that is no doubt due to my innate degeneracy and lack of moral compass, but probably also down to the fact that I tend to build worlds as wicked below as above. It's just that the above is safer for people.
that is: the dungeon is more dangerous for the same reason the night is more dangerous: less light.
To which I replied:
I see it more as being about different varieties of evil. You get evil on the overground but it's three-dimensional real evil like you get in our world: the people who perpetrate evil aren't doing it because they think it's evil, they're doing it because they misguidedly think it's the right thing to do. Even goblins. Maybe they're peeling the skin off you while you're still alive, but they're not doing it because they want to be evil, they're doing it because they enjoy it and, I dunno, maybe it's how you impress goblin chicks.
But in the depths of the underworld there is stuff that is just intrinsically evil for its own sake, or at least has motives so different to ours that we can't understand them and our only available analogue is what we call "evil". It's a mindset much more alien than the goblin skinning you alive, because at least the goblin has something in common with you: it knows what enjoyment is.
I wasn't quite sure what I meant by this at the time - the words seemed to spring forth from the aether that is my reptile brain - but I've been mulling it over and I think it can be boiled down to this.
The way I look at a D&D world, there are two kinds of evil. For the sake of reference, let's call them Evil 1 and Evil 2.
Evil 1 is what you might call "mundane evil". Everything that is mundanely evil is wicked, but basically has motives that can be understood and empathised with inasmuch as we can understand that people do absolutely awful things to one another but they still have reasons. Even the worst, most depraved serial killer has a reason for doing the things they do which is comprehensible on some level, no matter how sickening, and even if it just boils down to "I enjoy doing horrible things". We don't enjoy doing horrible things (or at least, I hope you don't), but we still know what it is to enjoy doing something. While this isn't much to have in common with the mindset of a serial killer, there is at least some shared frame of reference no matter how vague.
Thus, whether we're talking about an evil human sorcerer who lusts for power, an evil goblin who gets pleasure from causing pain, an evil banshee who hates the living, or an evil vampire who kills to sustain himself, we are still talking about things that are in some vague way comprehensible. We don't want to kill people by wailing at them like a banshee does, but we can sort of grasp at the reasons she has for doing so. (I should stress at this point that by "comprehensible", I do not for one second mean "excusable".)
The key here, is that in the Evil 1 category there are truly wicked and horrible creatures, but nobody does anything from a standpoint of BEING EVIL. Neither the sorcerer sacrificing a virgin to gain power, the goblin torturing you, the banshee wailing people to death, or the vampire drinking blood, are doing anything for the sake of being wicked. They are doing evil things for some other reason external to the wickedness (lust for power, sadism, hatred, hunger).
But in the depths of the underworld, and perhaps stalking the land above, there are things that do not even have the same frames of reference as us topsiders - these are things that commit acts of evil purely for the sake of being evil. This is what I call Evil 2: the entities whose motives are utterly incomprehensible and cannot therefore be explained beyond the rather inadequate formulation I have just given them. There is no point in trying to understand such beings, and no point in speculating about their thought processes; simply, they embody evil and wickedness - they are satan, in the ancient sense of being "the enemy". Any struggle with them will be a struggle to extinction, though they might not ever make their true nature known. I like a campaign setting which incorporates a notion of there being such entities, even in a sub-Lovecraftian sense, and they exist in Yoon-Suin, though in many different and unknown forms.