Circling back around, I understand why we want to have moral absolutes in D&D. If there is something that is evil, irredeemably and unalterably so, then it makes sense to kill it. There can be no argument, no quarter given, no moral qualms whatsoever about the just use of violence.
Only the Sith deal in absolutes.
To use the easiest example, if there is a demon that is unalterably evil, then destroying that demon must be good.
False logic. Slaughtering a Demon is only Good if you define 'Good' as 'the slaughter of Evil creatures.'
Thats not how I define moral goodness, it's not how the world generally defines moral goodness, and it's not how DnD has defined moral goodness for some time now.
DnD tends to define morally good as 'altruism, charity, mercy, compassion and self sacrifice'
Given D&D is a game that is inextricably tied into violence, then, there might be some questions raised when it is not a demon, but a human or humanoid; perhaps it is as simple as an 80s film, and in this fiction, by opposing the protagonist, they must be put to the sword. Or perhaps not.
DnD is a game of violence for sure.
But there are no 'questions raised'. If your PC are slaughtering things because they're there, or for no other reason than on the grounds of different race or ethnicity or social status or sexual orientation or differing cultures or gods (even evil ones), or killing out of fun or profit, then your PCs are
evil.
PCs of Neutral and Good alignments should only ever be resorting to violence when in self defence (collective or otherwise).
Seeing as nearly all monsters dont just sit there and offer PCs a cup of tea when the PCs encounter them; they tend to charge in breathing fire, swinging swords, trying to eat brains or otherwise kill the PCs in one of a billion horrible ways, this makes self defence a no-brainer.