but what do you mean when you say that I should_MattSimpson maximize your preferences?
I mean that according to my preferences, you, me, and everyone else should maximize them. If you ask what should_MattSimpson be done, the short answer is maximize my preferences. Similarly, if you ask what should_lukeproq be done, the short answer is to maximize your preferences. It doesn't matter who does the asking. If you ask should_agent should be done, you should maximize agent's preferences. There is no "should" only should_agent's. (Note, Eliezer calls should_human "should." I think it's an error of terminology, personally. It obscures his position somewhat).
We already have a term that matches Eliezer's use of "ought" and "should" quite nicely: it's called the "prudential ought." The term "moral ought" is usually applied to a different location in concept space, whether or not it successfully refers.
Then Eliezer's position is that all normativity is prudential normativity. But without the pop-culture connotations that come with this position. In other words, this doesn't mean you can "do whatever you want." You probably do, in fact, value other people, you're a human after all. So murdering them is not ok, even if you know you can get away with it. (Note that this last conclusion might be salvageable even if there is no should_human.)
As for why Eliezer (and others here) think there is a should_human (or that human values are similar enough to talk about such a thing), the essence of the argument rests on ev-psych, but I don't know the details beyond "ev-psych suggests that our minds would be very similar."
If you ask what should_MattSimpson be done, the short answer is maximize my preferences.
I find the talk of "should_MattSimpson" very unpersuasive given the availability of alternative phrasings such as "approved_MattSimpson" or "valued_MattSimpson". I have read below that EY discourages such talk, but it seems that's for different reasons than mine. Could someone please point me to at least one post in the sequence which (almost/kinda/sorta) motivates such phrasings?
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.