This is a linkpost for https://atheistkit.wordpress.com/ethics/
Would this be an accurate summary of what you think is the meta-ethics sequence? I feel that you captured the important bits but I also feel that we disagree on some aspects:
V(Elves, ) = Christmas spirity
V(Pebblesorters, ) = primality
V(Humans, _ ) = morality
If V(Humans, Alice) =/= V(Humans, ) that doesn't make morality subjective, it is rather indicating that Alice is behaving immoraly. V(Humans, ) (= morality) exists objectively insofar it is a computation instantiated by a class of agents at some point in time, but it is not a property of the world independent from the existence of any agents calculating it. Morality is there because of evolution, and it happens to be a complicated and somewhat unexplored landscape, which means that it's also fragile and possibly no one has a hold of it's entirety.
I think that's right.
Except that something is moral whether any being cares about morality or not, just like something is prime regardless of whether or not anyone cares about primality.
It's not that morality is there because of evolution, but that being who CARE about morality are there because of evolution.
I'm not sure what you mean by fragile morality, but since you've gotten pretty much everything right, I suspect you've got the right idea, there, too.