How about something like this: There's a certain set of semi abstract criteria that we call 'morality'. And we happen to be the sorts of beings that (for various reasons) happen to care about this morality stuff as opposed to caring about something else. should we care about morality? Well, what is meant by "should"? It sure seems like that's a term that we use to simply point to the same morality criteria/computation. In other words, "should we care about morality" seems to translate to "is it moral to care about morality" or "apply morality function to 'care about morality' and check the output"
It would seem also that the answer is yes, it is moral to care about morality.
Some other creatures might somewhere care about something other than morality. That's not a disagreement about any facts or theory or anything, it's simply that we care about morality and they may care about something like "maximize paperclip production" or whatever.
But, of course, morality is better than paper-clip-ality. (And, of course, when we say "better", we mean "in terms of those criteria we care about"... ie, morality again.)
It's not quite circular. Us and the paperclipper creatures wouldn't really disagree about anything. They'd say "turning all the matter in the solar system into paperclips is paperclipish", and we'd agree. We'd say "it's more moral not to do so", and they'd agree.
The catch is that they don't give a dingdong about morality, and we don't give a dingdong about paperclipishness. And indeed that does make us better. And if they scanned our minds to see what we mean by "better", they'd agree. But then, that criteria that we were referring to by the term "better" is simply not something the paperclippers care about.
"we happen to care about it" is not the justification. It's moral is the justification. It's just that our criteria for valid moral justification is, well... morality. Which is as it should be. etc etc.
Morality is seems to be an objective criteria. Actions can be judged good or bad in terms of morality. We simply happen to care about morality instead of something else. And this is indeed a good thing.
Oh shit. I get it. Morality exists outside of ourselves in the same way that paperclips exists outside clippies.
Babyeating is justified by some of the same impulses as baby saving: protecting ones own genetic line.
It's not necessarily as well motivated by the criteria of saving sentient creatures from pain, but you might be able to make an argument for it. Maybe if you took thhe opposite path and said not that pain was bad, but that sentience / long life/ grandchildren was good and baby eating was a "moral decision" for having grand children.
On Wei_Dai's complexity of values post, Toby Ord writes:
The kind of moral realist positions that apply Occam's razor to moral beliefs are a lot more extreme than most philosophers in the cited survey would sign up to, methinks. One such position that I used to have some degree of belief in is:
Strong Moral Realism: All (or perhaps just almost all) beings, human, alien or AI, when given sufficient computing power and the ability to learn science and get an accurate map-territory morphism, will agree on what physical state the universe ought to be transformed into, and therefore they will assist you in transforming it into this state.
But most modern philosophers who call themselves "realists" don't mean anything nearly this strong. They mean that that there are moral "facts", for varying definitions of "fact" that typically fade away into meaninglessness on closer examination, and actually make the same empirical predictions as antirealism.
Suppose you take up Eliezer's "realist" position. Arrangements of spacetime, matter and energy can be "good" in the sense that Eliezer has a "long-list" style definition of goodness up his sleeve, one that decides even contested object-level moral questions like whether abortion should be allowed or not, and then tests any arrangement of spacetime, matter and energy and notes to what extent it fits the criteria in Eliezer's long list, and then decrees goodness or not (possibly with a scalar rather than binary value).
This kind of "moral realism" behaves, to all extents and purposes, like antirealism.
I might compare the situation to Eliezer's blegg post: it may be that moral philosophers have a mental category for "fact" that seems to be allowed to have a value even once all of the empirically grounded surrounding concepts have been fixed. These might be concepts such as "would aliens also think this thing?", "Can it be discovered by an independent agent who hasn't communicated with you?", "Do we apply Occam's razor?", etc.
Moral beliefs might work better when they have a Grand Badge Of Authority attached to them. Once all the empirically falsifiable candidates for the Grand Badge Of Authority have been falsified, the only one left is the ungrounded category marker itself, and some people like to stick this on their object level morals and call themselves "realists".
Personally, I prefer to call a spade a spade, but I don't want to get into an argument about the value of an ungrounded category marker. Suffice it to say that for any practical matter, the only parts of the map we should argue about are parts that map-onto a part of the territory.