So this is how my thinking has moved and evolved, to the point I'm comfortable with now.
"Evil" can be used to describe tendencies in certain beings, innately or circumstantially. A few examples of what I mean:
"Cultural Evil" (goblins, orcs, drow, etc) Creatures that, for reasons usually pertaining the specific cultures they are raised in, end up evil. This can be due to societal traits, influence of extraplanar entities, or deities, or simply victims of circumstance (if we cannot inspire love, we will inspire fear). It is completely possible for individuals and groups to either rebel against such factors or be raised outside of them and end up with alignments that wouldn't be viewed as evil. There is nothing innate about their evilness.
"Malevolent Evil" (fiends, undead, fey) are born or created with evil intent. They are beings that are either created by evil forces (like fiends), evil magic (necromancy) or strong negative emotion (evil fey). While occasionally one of these beings does change from its innate programming, they are rare beings and exceptions that prove the rule.
"Amoral Evil" (dragons, aberrations, some monstrosities) are creatures that don't work on the same morality scale as humanoids, be it they view themselves superior to such concepts (dragons) or it is utterly alien to them. They act evil in the eyes of others, but it's because their morality scales don't see problems with the same things you or I would.
"Unaligned" is for beings that are not capable of sentient thought. Beasts, Plants, or Constructs are don't think it terms of morals, only following orders or acting on instinct.
It is completely possible to have drow slavers attack a town and still not make all drow evil, a good-aligned succubus existing doesn't mean demons are going to be your friend, and mind flayers cannot understand why you can't raise humans in pens to be bred and used for food.