So, for the record, humanoids can't be inherently evil - but supernatural beings can?
Again, I have no problem with this. But there is an obvious bias here coming into play. It is as if supernatural beings can't have freewill, yet examples abound in D&D of just that. Therefore, can you see where one side of the debate might just decide to pull their rope a little in the mortal direction?
It makes zero sense for a biological entity to be inherently evil. D&D humanoids are K-strategies, which means they have only one or a few young, which have a relatively longish maturation period and thus need to be cared for; they aren't r-strategists (unless you're using Space Fungus orcs instead of the typical D&D orcs). They need to eat and create tools and comfort objects like clothing, but they can't create it all themselves so they have to live in groups. They live in groups which means they need to be able to work in a group. They have societies, which means that they need to be able to work to keep the society stable or to improve it. If they were Always Evil, they would lack the ability to do any of the above for any period of time, and they would have died out ages ago, their evil having cause them to implode.
Supernatural creatures--fey, fiends, elementals, undead--are, in fact,
supernatural. They are made of or animated by magic. They don't obey natural laws. Most of them don't
have to reproduce; they are literally born out of their surroundings (lots of fey are created due to strong emotions and others seem to spring from nature itself, fiends are formed out of evil souls or directly created by more powerful fiends or gods, and most elementals seem to spring up from primal matter) and even those who
do reproduce (like vampires, some fey, and some fiends) generally do so for either emotional reasons or to create minions, not because they are trying to keep their species in existence. Most of them either don't need to eat or have the type of diet where it doesn't pay to work with others to satisfy, because they need something like blood. Many of them are also immortal, or close to it, and as such they don't
think like humanoids do. Heck, in many ways, there aren't even true "races" of supernatural beings. Statblocks aside, it's pretty fair to say that each demon is its own entity and is unrelated to any other demon, even if they have the same statblock--after all, they don't share a common ancestor since one could have come from a larva formed by an evil human on Toril and the other could have been created by a bored demon prince using a soul that he stole from a hapless good-aligned gnome from Oerth.
So yeah. I'm sure there are plenty of examples non-evil supernatural beings. But that's completely different than what I'm talking about.