We have intutions that certain things are wrong -- murder, robbery and so forth -- and we have the intution that those things are wrong, not just wrong-for-peope-that-don't-like-them. This intuition of objectivity is what makes ethics a problem, in conjunction with the absence of obvious moral objects as part of the furniture of the world.
ETA: again, a defence of moral subjectivism seems to be needed as part of CEV..
Traditional moral subjectivism usually says that what X should do depends on who X is in some intrinsic way. In other words, when you ask "what should X do?", the answer you get is the answer to "what should_X X do?" On EY's theory, when you ask "what should X do?", the answer you get is the answer to "what should_Y X do?" where Y is constant across all X's. So "should" is a rigid designator -- is corresponds to the same set of values no matter who we're asking about.
Now the subjectivity may appear to come ...
In You Provably Can't Trust Yourself, Eliezer tried to figured out why his audience didn't understand his meta-ethics sequence even after they had followed him through philosophy of language and quantum physics. Meta-ethics is my specialty, and I can't figure out what Eliezer's meta-ethical position is. And at least at this point, professionals like Robin Hanson and Toby Ord couldn't figure it out, either.
Part of the problem is that because Eliezer has gotten little value from professional philosophy, he writes about morality in a highly idiosyncratic way, using terms that would require reading hundreds of posts to understand. I might understand Eliezer's meta-ethics better if he would just cough up his positions on standard meta-ethical debates like cognitivism, motivation, the sources of normativity, moral epistemology, and so on. Nick Beckstead recently told me he thinks Eliezer's meta-ethical views are similar to those of Michael Smith, but I'm not seeing it.
If you think you can help me (and others) understand Eliezer's meta-ethical theory, please leave a comment!
Update: This comment by Richard Chappell made sense of Eliezer's meta-ethics for me.