Where did he?
For example, here. Read the whole thing, not just this illustrative quote:
I don't think that human morality is arbitrary at all, and I would expect any logically omniscient reasoner to agree with me on that.
That's a part of the metaethics sequence, to which this posting might be a suitable entry point, which says where he's going, and tells you what to read before going there.
Less Wrong is extremely intimidating to newcomers and as pointed out by Academian something that would help is a document in FAQ form intended for newcomers. Later we can decide how to best deliver that document to new Less Wrongers, but for now we can edit the existing (narrow) FAQ to make the site less scary and the standards more evident.
Go ahead and make bold edits to the FAQ wiki page or use this post to discuss possible FAQs and answers in agonizing detail.