That's somewhat arguable.
There are cases of Angels "falling" and a case of a Succubus Paladin in D&D lore. This would seem to imply there is some possibility that any D&D creature could be "good."
Which isn't to say that I think you're wrong. I'm simply attempting to explore the mental space of how this discussion appears to be approaching the subject.
It has also been suggested by others that we should ignore the established in-game/in-world way things work and judge things through the lens of our real-life world.
Does that lead to PCs being evil?
PCs tend toward killing creatures and hoarding wealth.
This is exactly the problem with engaging with that asinine, backward, distraction of an argument about demons. It does not matter, but it is becoming what the thread is about anyway, purely via repetition.
It’s pure BS whataboutist nonsense.
As for the “are PCs evil” thing, it depends on what they’re actually doing. I’ve never played in or run a game of D&D where the PCs just went into old ruins full of sentient people to genocide them and take their stuff.
That sort of thing isn’t what modern D&D adventures are written to be about, either.
Instead, PCs are solving problems. Raiders are attacking villages. The PCs are hired to stop them. The PCs get a reward and also get to keep any valuables they find, hopefully returning at least some of it to those it was taken from, but the villagers know when they agree to the terms that the somewhat merc PCs will probably keep the good stuff.
Or, my current rogue PC is an adventurer because a Wizard killed his ships crew in order to make them his undead thralls in order to win a fight with another Wizard over territory, and that Wizard then became a lich, and is at the head of a cult that seeks to end the world in demonic fire and rule over the ashes.
Treasure is very much a secondary concern.
The PCs of Dragonlance are trying to save the world from evil dragon armies and bring back the gods.