I don't know why you are bringing up hedonism. It is bad to kill even if you enjoy it; so if morally good means what it is good to do, as I say, it will be morally bad to kill even if it is pleasant to someone.

The fully intersubjective but non-objective theory of meaning that you are suggesting is also false, since if everyone all at once agrees to call all dogs and cats "dogs", that will not mean that suddenly there is no objective difference between the things that used to be called dogs and the things that used to be called cats.

The correct theory is this:

"Dog" means something that has what is in common to the things that are normally called dogs. Notice that this incorporates inter-subjectivity and convention, since "things that are normally called dogs" means normally called that by normal people. But it also includes an objective element, namely "what is in common."

Now someone could say, "Well, what those things have in common is that people normally call them dogs. They don't have anything else in common. So this theory reduces to the same thing: dogs are what people call dogs."

But they would be wrong, since obviously there are plenty of other things that dogs have in common, and where they differ from cats, which do not depend on anyone calling them anything.

The correct theory of goodness is analagous:

"Good" means something that has what is in common to the things that are normally called good. Again, this incorporates the element of convention, in "normally called good," but it also includes an objective element, in "what is in common."

As before, someone might say that actually they have nothing in common except the name. But again that would be wrong.

More plausibly, though, someone might say that actually what they have in common is that people desire them. And in a sense this is Eliezer's view. But this is also wrong. Let me explain why.

One difficulty is that people are rarely wrong about whether something is a dog, but they are often wrong about whether something is good. This makes no difference to the fact that the words have meanings, but it makes it easier to see what is "normally called a dog" than "normally called good." If someone calls something good because they are mistaken about it in some way, for example, then you cannot include that as one of the things that has what is in common, just as if someone mistakenly calls a cat a dog in some case, you cannot include that cat in determining what dogs have in common.

Just as it is not too difficult to see that dogs have some objective features that distinguish them from cats, good things have an objective feature that distinguishes them from bad things: good things tend to result in things desiring them, and bad things tend to result in things avoiding them. Now that tendency is not complete and perfect, especially because of people making mistakes. So occasionally someone desires something bad, or avoids something good. But the general tendency is for good things to result in desire, and bad things to result in avoidance.

Now if you think reality is intrinsically indifferent, as Eliezer does, then you would say that there is no such tendency: people have a tendency to desire some things and avoid others. We then call the things we tend to desire, "good," and the things we tend to avoid, "bad," but actually the good things have nothing in common except that we are desiring them, and the bad things have nothing in common except that we are avoiding them.

As you pointed out yourself, people have an inherent instinct to deny this position. That is because people ask, "why do I desire these things, and not others?" And they want the answer to be, "Because these are good, and the others are not." And that answer does not make sense, unless the good things have something objective in common in addition to the fact that I desire them.

The instinct is correct, and Eliezer is wrong, and we can prove that by finding some things that the good things have in common, other than desire. The way to do that is to note that desire itself is a particular case of something more general, namely a tendency to do something. And the tendencies to do something that we find have various properties. So for example consistency is one of them -- without consistency, you cannot have a tendency at all. Rocks tend to fall, and it is very consistent that they go downwards. And note that without this consistency, there would be no tendency. Likewise, tendencies will always preserve the existence of something -- not necessarily of the whole existence of the thing which immediately has the tendency, but of something. Thus inertia is a tendency to motion, and it tends to preserve the amount of that movement. And we could go on. But all of these things imply that "what we desire" has various properties in common besides the fact that we desire it. And this is what it is to be good.