I'm only halfway through this thread, but I will throw my 2cp in.
Personally, I don't like the 'solution' of moving humanoid creatures to other types. I have heard the official reason, but honestly probably couldn't repeat it accurately. Something about 'they fit better there'. As stated, I disagree, and it seems dishonest. It sounds like there are people on both sides of the fence believe they did it for moral reasons. There is, apparently, a belief that it is 'problematic'* that humanoids have a default alignment and that by making them fae, elemental, fiend, or whatever, that makes that okay.
Specifically on the topic of Evil Orcs, I play them that they are humanoid, they do have free will, but their free will is limited. D&D is a fantasy game, and there is more than genetics at work. Evil (capital E) is a real thing. It can be detected and measured. Gods actually exist and can be proven to exist. You can talk to them, and they talk back. You can even go visit them if you are powerful enough. So, if there is an actual real god (albeit in a make-believe world) that is Evil, and that god creates a species** then that god can create them however they want. In this case Gruumsh created Orcs and they are afflicted by his mark.
In the 2014 PHB, under half-orc it talks about the mark:
"The one-eyed god Gruumsh—lord of war and fury—created the first orcs, and even those orcs who turn away from his worship carry his blessings of might and endurance. The same is true of half-orcs. Some half-orcs hear the whispers of Gruumsh in their dreams, calling them to unleash the rage that simmers within them."
And that answers it right there. Gruumsh does bless the species he created with might and endurance, but he also influences their behavior. Orcs are violent because Gruumsh created them with powerful emotions and encourages them to unleash their rage. He glories in the violence that they perpetrate... Because he is EVIL!
Same with Lolth and Drow. Their goddess is Evil and she influences her people to be Evil. Because magic.
It’s not genetics. It’s not culture. It’s magic.
Anyway, that is my explanation for ‘usually Evil’ species. If you can get them away from the supernatural Evil that influences them, then they can choose to be Good. Of course, since they have free will, they might still choose to be Evil, but that is their choice.
*Saying something is problematic isn't a statement of objective fact. You can't just say something is problematic and expect everyone to agree. You have to explain why something is problematic.
**I agree with the change of race to species. I understand the argument that species is 'a little too high-tech', and I agree, but the fact is that other sentient species do not exist in the real world, so ancient humans had no need to create a word for them. If you look at the word race as in The Human Race, then having other races like elves and orcs makes sense, However, it has also been used to separate humans from other humans, which doesn't make sense. So yeah, species just makes it clearer.