D&D is not the real world, and need not have real world standards.
Stated like this, it's like saying "D&D is not the real world, and need not have real world mathematics". The sentence can be uttered, but what does it mean? What does it mean, for instance, to say that in D&D the square root of 9 is not 3 but 2? Of that if I lie two 10' poles end-to-end, the resulting length is 15' and not 20'.
So if, in the D&D world, humans and other intelligent beings are as close to real-world human beings as the game rules suggest, and if real-world human beings have an interest in being alive that underpins some sort of right to life, that is defeasible in some circumstances (eg self-defence) but not in others (eg "I really don't like the look of you!"), then how would the game-world humans and similar intelligent beings be different?
Nothing in your discussion of any of the hypothetical cases that has come up - eating babies, torturing and killing prisoners, etc - makes me think that you are bringing to bear any standards different from those that are at stake in the real world. And for good reason - the situations are relevantly different.
And the rulebooks bear this out. The 2nd ed AD&D PHB says that good characters "are just that" ie good. Where "good" is clearly being used in its ordinary sense.
The 3.5 SRD says that ""Good" implies altruism, respect for life, and a concern for the dignity of sentient beings. Good characters make personal sacrifices to help others." This sets out a standard for goodness which is obviously grounded in real world standards: other regard, extending to a willingness to make personal sacrifices to help others, is key to ordinary conceptions of morality, and distinguishes moral sensibility from selfishness, amoralism and sociopathy; respect for life and concern for the dignity of sentient beings are key values of enlightenment morality, as expressed (for instance) in the Declaration of Independence and the UDHR.
*****
Part of what I prefer about spectrum-style L-N-C or 4e alignment is that it makes it easier to understand the motivations of those at the "wrong" end of the spectrum. Why, for instance, do agents of chaos (in 4e, say, that would be primordials and demons) pursue the dissolution of creation without regard for the lives and dignity of those beings whose lives are part of that creation? It's not because they "have no compassion for others and kill without qualms if doing so is convenient", nor because they "[kill] for sport" (which is how the 3.5 SRC characterises evil). It's because they think there are other values in play - free expression and creativity, even entropy itself as a value - besides with the interests in life and dignity of sentient beings pale into insignificance. From the standpoint of the typical game participant, and of the typical character in the gameworld, such views might be wrong, even (in a certain sense crazy), but they at least establish a framework within which we can make sense of these beings as (by their own lights) rationally motivated. We can also imagine them as having a certain sort of cognitive bias - because they are so committed to their project of re-creation of the world, they fail to notice the significance of the lives and interests of the sentient beings living in this world here and now. That is a cognitive bias that is familiar to us from the real world, among Soviet planners, National Socialist demographers, imperial bureaucrats, even social security officials and parking inspectors.
Because of this, even if I dispense with the labels as unhelpful (which I do) at least I know how I am meant to envisage a primordial, or a fire giant who serves one, being motivated.
As I was discussing not far upthread with [MENTION=16726]jsaving[/MENTION], one of my problems with 9-point alignment is that it decouples moral concerns of the sort obviously in play with Good and Evil from social theoretic conceptions, in ways that make no sense at all - for instance, I'm supposed to imagine that it can be true that both a person who is committed to dissolution of all social bonds, and a stalwart conservative, can both be equally serving "the dignity of all sentient beings". That makes no sense at all: whoever has the right of it in an imagined debate between (say) Edmund Burke and Milton Friedman about what is the best way to serve the dignity of all sentient beings, they can't both be correct.
jsaving suggested is that perhaps what alignment measure is hopes/convictions rather than realities, but then it seems that a couple of commune spells could settle the issue ("What sorts of economic and political arrangements will best serve the dignity of all sentient beings?") and also it seems that very few people are going to turn out to be evil (most selfish people tend to
think that they're serving the interests of others; they're sincere but self-deluded).
***************
But anyway, I don't see how I'm possibly meant to work any of this out without having regard to the real world. Bracket parts of the real world, sure - I'm happy to run a D&D game in which we ignore all the socio-economic reality that explains why, in a feudal economy, it can be very hard for peasants to life a life of equal dignity - but this is not bracketing the standards by which we measure and understand these morality of these phenomena. With those bracketed, how are we meant to make sense of anything at all?
I mean, how would anyone make sense of the phrase "respect for ilfe" other than by thinking about the real-world meaning of that phrase?