I don't think that adequately addresses lukeprog's concern. Even granting that one person shouldn't have the privilege of deciding the world's fate, nor should an AI be created for every human to fight it out (although personally I don't think an would-be FAI designer should rule these out as possible solutions just yet), that leaves many other possibilities for how to decide what to do with the world. I think the proper name for this problem is "should_AI_designer", not "should_human", and you need some other argument to justify the position that it makes sense to talk about "should_human".
I think Eliezer's own argument is given here:
Between neurologically intact humans, there is indeed much cause to hope for overlap and coherence; and a great and reasonable doubt as to whether any present disagreement is really unresolvable, even it seems to be about "values". The obvious reason for hope is the psychological unity of humankind, and the intuitions of symmetry, universalizability, and simplicity that we execute in the course of our moral arguments.
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.