What I'm failing to see is why it matters.
Ok, going back to the start of this side trek, the topic was, "In a particular DM's campaign, what is the definition of an 'orc'?" To simplify the discussion, I said that we could lump pretty much all definitions into one of two groups. Either orcs are people, or orcs are demons.
If orcs are people, then orcs are capable of both good and evil, and individual orcs should be primarily judged by their actions, and not the fact that they are orcs. If orcs are people, then it is at least possible that the fact that they are CE is a result of nurturing rather than inherent racial destiny, and an orc raised outside of a culture of violence and cruelty might adopt less evil ways, and likewise an orc exposed to new experiences might repent or reform their ways. Orcs in other words, because they are people might be predisposed to evil, but would not be evil inevitably.
But if orcs are demons, then orcs are not capable of both good and evil. The fact that you know an individual is an orc is sufficient reason to believe that the orc is not merely misguided, but wholly evil and wholly ruined. A demon is not evil because of its nurture, but as a result of its inescapable nature. You can't reform a demon. You can't convert a demon. A demon cannot learn from its experiences and repent. A demon can't be raised to be something other than a demon. Since demons are literally made of evil, any attempt to cleanse a demon of evil requires destroying the demon completely and replacing it with something that is ultimately no longer a demon.
So I brought up earlier that beginning in 3e, the D&D game began to suggest overtly in the entries that even though orcs and demons were both Chaotic Evil, that they weren't the same sort of chaotic evil. Orcs became mechanically humanoids that were
usually Chaotic Evil, where as demons were outsiders that were
always Chaotic Evil. Even though they shared the same alignment, the game was stating that despite this, they could be differentiated because the entry specifically added new keywords to each monster entry's alignment description. The mechanics of an orc began to express the idea of orcs being people, and not demons.
The global caveat at the front of the book in 2e which you claimed made me wrong about this, in fact doesn't express the idea that orcs and demons are different, since it applies to them equally. Thus, your statement that my claim was not accurate, was made on the basis of not understanding what my claim was or why it was important. In fact, as you've continued to defend your claim that my claim was not accurate, you've repeatedly undermined your own argument by admitting the very facts that make my original claim accurate.
I don't think it's relevant. Alignment has never, in any edition, differentiated monsters of the same alignment.
Yes, but it very much matters whether a CE being is a person, or a demon. If the CE being is a person, it has the rights and dignities due to a person, for example (assuming you are CG) it would be subject since you are also a person to the ethic of reciprocity - "Do unto others what you would have them do unto you." But if the CE being is a demon, it isn't is a "you", but an evil thing without rights and dignities owed it. Early D&D tended to define "orc" as being essentially a lesser sort of demonic creature, suitable for encountering on the first level of dungeon, and the question of the orcs personhood was either generally not brought up or answered decidedly in the negative. (Compare Trollocs in 'Eye of the World' or the Goatmen in Diablo.) This is in keeping with the role that they played in Tolkien's legendarium. However, as D&D evolved, people began to more and more treat every intelligent race as being a person. This actually reached it height in late 2e, when even demons tended to be defined as people (for example, see Planescape:Torment), ultimately defining demon out of existence. In 3e however, and even more so in 5e, there has been an explicit separation of evil monsters into two groups, those that are, though evil, still people, and those that are demons.
As a side note, this explicit separation parallels a decision I made in the late 1980's about my homebrew campaign, when I officially made goblins into a sort of "person" sharing a common backstory with elves, humans, dwarves, orine, and idreth ("free peoples"), but moved races like gnolls, kobolds, minotaurs and the like into a completely different group with a completely different backstory ("lesser servitors"). Thus, goblins are certainly people, but gnolls are certainly demons and in my campaign a philosopher could explain why and anyone with enough ranks in Know (Religion) actually knows why. To put it briefly, goblins have free will and gnolls do not.
Similar behavior does not equate to a connection.
Things are connected if they have the same fundamental nature, or to put it another way, if things have the same fundamental origin. For example, a famous declaration of that principle is, "We hold these truths to be self evident, that all men are created equal, and are endowed by their Creator with certain inalienable rights..." In other words, all men are connected by their common origin, nature, and purpose. If orcs have a common origin and nature with humanity, then they are likely to have the same inalienable rights. But we cannot make the same assertion about things that do not have the same nature or purpose as humanity. They would have their own separate nature and inherent rights. The more dissimilar the natures, the more different you'd expect those rights to be.
Or in other words, depending on the backstory we give to orcs, we can define them as persons who should be treated as persons, or as monsters that should be treated as monsters. Since outside of Green Ronin's "Book of the Righteous", D&D has tended to be very vague on cosmological backstory and its implications, we can't expect any two tables to in any way agree on the definition of "orc". We can make assertions about what sort of definition a table is likely adopt on the basis of which edition was current when they started play, but even then that would be more of a 'usually' than an 'always' case.