Moral realism claims that:
[True ethical propositions] are made true by objective features of the world, independent of subjective opinion.
Moral realists have spilled oceans of ink justifying that claim. One common argument invents new meanings for the word "true" ("it's not true the way physical fact, or inductive physical law, or mathematical theorems are true, but it's still true! How do you know there aren't more kinds of truth-ness in the world?") They commit, in my experience, a multitude of sins - of epistemology, rationality, and discourse.
I asked myself: why do some people even talk about moral realism? What brings this idea to their minds in the first place? As far as I can see, this is due to introspection (the way their moral intuitions feel to them), rather than inspection of the external world (in which the objective morals are alleged to exist). Materialistically, this approach is suspect. An alien philosopher with different, or no, moral intuitions would not come up with the idea of an objective ethics no matter how much they investigated physics or logic. (This is, of course, not conclusive evidence on its own that moral realism is wrong. The conclusive evidence is that there is no good argument for it. This merely explains why people spend time talking about it.)
Apart from being wrong, I called moral realism dangerous because - in my personal experience - it is correlated with motivated, irrational arguments. And also because it is associated with multiple ways of using words contrary to their normal meaning, sometimes without making this clear to all participants in a conversation.
As for Eliezer, his metaethics certainly doesn't support moral realism (under the above definition). A major point of that sequence is exactly that there is no purely objective ethics that is independent of the ethical actor. In his words, there is no universal argument that would convince "even a ghost of perfect emptiness".
However, he apparently wishes to reclaim the word "right" or "true" and be able to say that his ethics are "right". So he presents an argument that these words, as already used, naturally apply to his ethics, even though they are not better than a paperclipper's ethics in an "objective" sense. The argument is not wrong on its own terms, but I think the goal is wrong: being able to say our ethics are "right" or "true" or "correct" only serves to confuse the debate. (On this point many disagree with me.)
I write all this to make sure there is no misunderstanding over the terms used - as there had been in some previous discussions I took part in.
I can't understand why you would be here arguing about a moral question in the first place if you thought there was no answer.
Certainly there are answers to moral questions. However, they are the answers we give. An alien might give different answers. We don't care morally that it would, because these are our morals, even if others disagree.
Debate about moral questions relies on the facts that 1) humans share many (most?) moral intuitions and conclusions, and some moral heuristics appear almost universal regardless of culture; and 2) within that framework, humans can sometimes convince one another to change their moral positions, especially when the new moral stand is that of a whole movement or society.
Those are not facts about some objective, independently existing morals. They are facts about human behavior.
As to how I determined that opinion, I imagined the overall negative effects of being exterminated or sent to a concentration camp, imagined the fleeting sense of happiness in knowing someone I hate is suffering pain, and then did the moral equivalent of estimating how many grains of rice one could pile up on a football field (i.e. made a guess). This is just my current best algorithm though, I make no claims of it being the ultimate moral test process.
You start the way we all do - by relying on personal moral intuition. But then you say there exists, or may exist, an "ultimate moral test process". Is that supposed to be something independent of yourself? Or does it just represent the way your moral intuitions may/will evolve in the future?
Well, this seems to be a bigger debate than I thought I was getting into. It's tangential to any point I was actually trying to make, but it's interesting enough that I'll bite.
I'll try and give you a description of my point of view so that you can target it directly, as nothing you've given me so far has really put much of a dent in it. So far I just feel like I'm suffering from guilt by association - there's people out there saying "morality is defined as God's will", and as soon as I suggest it's anything other than some correlated preferences...
This is based on a discussion in #lesswrong a few months back, and I am not sure how to resolve it.
Setup: suppose the world is populated by two groups of people, one just wants to be left alone (labeled Jews), the other group hates the first one with passion and want them dead (labeled Nazis). The second group is otherwise just as "good" as the first one (loves their relatives, their country and is known to be in general quite rational). They just can't help but hate the other guys (this condition is to forestall the objections like "Nazis ought to change their terminal values"). Maybe the shape of Jewish noses just creeps the hell out of them, or something. Let's just assume, for the sake of argument, that there is no changing that hatred.
Is it rational to exterminate the Jews to improve the Nazi's quality of life? Well, this seems like a silly question. Of course not! Now, what if there are many more Nazis than Jews? Is there a number large enough where exterminating Jews would be a net positive utility for the world? Umm... Not sure... I'd like to think that probably not, human life is sacred! What if some day their society invents immortality, then every death is like an extremely large (infinite?) negative utility!
Fine then, not exterminating. Just send them all to concentration camps, where they will suffer in misery and probably have a shorter lifespan than they would otherwise. This is not an ideal solutions from the Nazi point of view, but it makes them feel a little bit better. And now the utilities are unquestionably comparable, so if there are billions of Nazis and only a handful of Jews, the overall suffering decreases when the Jews are sent to the camps.
This logic is completely analogous to that in the dust specks vs torture discussions, only my "little XML labels", to quote Eliezer, make it more emotionally charged. Thus, if you are a utilitarian anti-specker, you ought to decide that, barring changing Nazi's terminal value of hating Jews, the rational behavior is to herd the Jews into concentration camps, or possibly even exterminate them, provided there are enough Nazi's in the world who benefit from it.
This is quite a repugnant conclusion, and I don't see a way of fixing it the way the original one is fixed (to paraphrase Eliezer, "only lives worth celebrating are worth creating").
EDIT: Thanks to CronoDAS for pointing out that this is known as the 1000 Sadists problem. Once I had this term, I found that lukeprog has mentioned it on his old blog.