Why are orcs being inherently evil different than Demons/Devils/Angels/Werewolves/Slaadi?
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And how are orcs made? Two orcs have sex and have a baby.
Note something about that? Orcs are the only one on the list that start as an infant. Every single other creature you named, they don't grow up, they don't start as a baby. They are formed, fully mature and ready to fulfill their role. That is why Orcs being inherently evil is a bigger problem than any of the other creatures you listed.
I still don't have an issue with saying, "the entire race of orcs was formed from the bile of Gruumsh and filled with hate." And, by "don't have a problem" I mean that I would not find it unacceptable if a GM did that in their game. That is, more or less, the original lore. Orcs are bad because they are filled with an uncontrollable hate that comes from a god. They are given humanoid form and biology, but that hate is deeply ingrained.
As far as them being born "the normal way", well, they wouldn't be the only species prone to eating their young. There are also plenty of species with traits bred into them. Wolves are pack animals. Herding dogs herd (oh good lord does my puppy herd the poor cats). Birds migrate. The scorpion stings the fox.
You don't have to use it, but it's not wrong for someone to do so.
Not really, in the same vein I was just talking about, think about Gnolls for a second. Why are Gnolls different from orcs? Because a new gnoll is only born when a hyena eats the corpse of a humanoid murdered by a gnoll. Again, they are created fully formed, that is a big difference.
Eh? Where did that come from? In 37 years of playing D&D, I've never heard it. I mean, it's not a bad story, but I've just never heard it.
I've always assumed that anything with the "humanoid", "monstrous humanoid" (when it exists), or "giant" tags pretty much went through the same sort of real-world sexual reproduction as humans.
So, is a half-Orc a person?
I'm not a fan of half-elves and half-orcs. They're just... odd. The less human-centric the world, the less they make sense. They worked in Tolkien because humans were the center of everything. Elves were so blessed that they could breed with humans and orcs were corrupted elves.
In D&D, I'd say the half-orcs have humanity and are more nurture than nature. That's why they make sense as a PC race. Orcs should not be playable in settings where they are "born bad".