Our world = Evil people are those who like evil actions and/or are addicted to them. They can change at any time, but they don't because they like evil actions. There is no nature or dark energy making them crave evil. They chose to enjoy it, and they continue to enjoy it.
Fantasy worlds = Evil is represented by actual forces such as evil spirits, the Shadow Weave, gods and evil creatures, like dragons. Evil magic can corrupt and literally change people so they have no choice but to become evil. This was literally the premise of BG1 and 2. You were fighting the powerful corruption heritage within you.
D&D is built upon alignment systems. As you aquire items, you atune yourself to them, but only if you share the alignment. A good person carrying a corrupt artifact may find themselves being corrupted.
So, in fantasy, an entire race can literally be evil because the race as a whole is attuned to evil.
You are certainly welcome to your opinion of what makes good fantasy. I personally find the notion of "metaphysical evil" to be incoherent and I welcome changes that move away from this. Sapient beings can choose their actions, and should therefor be held responsible for what they do or do not do and not for some idealized concept of evil that is associated with their lineage.
The essence of fantasy is that it is LIKE reality, but it is not reality. Each fantasy world is built on certain fantastic elements. "The Light Side creates life. The Dark Side destroys and corrupts."
In D&D, Alignment has ALWAYS been what the worlds have been built on. Even the gods are subject to alignment. They do not rule the alignments. They are locked into them. It is the foundation of the entire game system's stories across various worlds, not just Forgotten Realms. Take this away, and you tear out the foundation for the entire game.
Again, this is not Star Wars or Star Trek or Skyrim or whatever where every race is capable of being good or evil. That's one of the things that has always set D&D apart. You have good, evil and neutral, and those alignments set the foundation for gameplay. If I'm good, and I encounter evil, I know I can just kill it because it's evil. I don't have to worry about whether I'm killing someone's dad or brother or cousin or whatever. It's bad. End of story. Cast a spell to know alignment, learn it's bad, kill it.
Start making every monster sentient with the potential to be redeemed or good and I will certainly have a problem wanting to purge the world of anything because, well, "they might just be misunderstood."
Baby dragon is eating children in a local village. I go to kill it. It tells me, "But, I have no food, Sir.". Big soulful eyes. "Please Sir. I'm just so hungry. Please don't kill me."
"Lying wyrm! Eat chickens and cows. Not people. Die!"
"I didn't know better. I'm just a kid. Please Sir."
What the flip do I do? Let it live just because it's "misunderstood?". It was eating children!
But it's just so child-like and seems good, and, well, it could be good if raised right.
Well. Sucks to be the parents of those dead kids. I'm gonna keep the monster and raise it myself, cause it MIGHT be good. Maybe.
