I was responding to @Clint_L who, if I understood correctly, stated we can not have objective morals in game, because morals in the real world are ultimately subjective. I was pointing out that, even if the latter is true, it does not necessarily imply you can not explore a fiction in which objective morals exist, by providing a prescription for what Good, Evil, etc. mean within the context of that fiction.The issue of what it means for things to be "objectively evil" is a fairly complicated one in metaphysics and philosophy of language. I'm going to try and keep out of it in this thread!
But the idea that putting milk in tea in Tuesday in July might be the epitome of evil seems ridiculous to me. Evil isn't an arbitrary notion, an empty vessel into which anything can be poured. Good is connected to values, to human interests (and rights, if such things exist), to the wellbeing of others. Evil is the opposite of these things - indifference to value and the interests of others, in pursuit of self-interest.
It has nothing to do with putting milk in tea as such. For whatever reason, there might be a taboo against doing such a thing. But if it's evil to do that, that would be because of a promise or an obligation imposed by someone else - maybe a god. The god, in turn, presumably would have a reason for imposing such an obligation. The wrongdoing wouldn't be the putting of the milk in the tea, but the breaking of the promise or the disobedience to authority.
You seem to hold to an objective description of good, evil, etc., and disagree with the hyperbolic example I gave. Which, fine, I'm not trying to suggest a universal alignment system for D&D. Rather I was trying to express something similar to your last paragraph. In D&D we do have absolute authority figures, the DM and, to some extent, the players who are the ones that get to say what constitutes good and evil.
But is exactly what we can do in fiction. A large part of scifi basically boils down to saying some circles are squares*. Proximity to a nuclear detonation gives you cancer, not make you transform into an invulnerable giant when you get angry. Mutations in your DNA are unlikely to make you able to control weather. It's clearly a matter of personal taste, but to me being on board with these is no different than being on board with ad-hoc definition of alignments.I agree with @Crimson Longinus on this. It makes no sense. It's like positing that, in my fantasy world, some circles are square.
*The Orthogonal trilogy of novels by Greg Egan is IMO one of the most well-executed examples of this. The everyday laws of nature in that universe are so fundamentally different from those of our own reality to the point that he wrote several dozen pages working out how physics would change in that universe.