The argument wouldn't involve running hot water in your house, but would involve things like social cohesion, shared values, psychological satisfaction, etc.
Think about meme evolution and selection criteria. Religion is a very powerful meme that was strongly selected for. It certainly provided benefits for societies and individuals.
There seems to be a widespread impression that the metaethics sequence was not very successful as an explanation of Eliezer Yudkowsky's views. It even says so on the wiki. And frankly, I'm puzzled by this... hence the "apparently" in this post's title. When I read the metaethics sequence, it seemed to make perfect sense to me. I can think of a couple things that may have made me different from the average OB/LW reader in this regard: