Where do atheists get their morality from?

[Whateverist]

First, our wills are not radically free. What we as an evolved biological organism are capable of willing, what we find hard to will and what is easy, is defined as an artifact of our evolutionary history. Our wills have been refined over time to serve the needs of our selfish genes. And something peculiar about that will, is that it deviates significantly from rational models. ... Moreover, a large chunk of our will involves cooperative ventures like families, tribes, and societies, ventures in which our evolved psychology allows us to leverage language, culture and reason into assemblages which include things like agreeing to be punished if we break rules, and so forth, which result in a sophisticated will which takes many things beyond visceral desire into account.

Second is that our wills are what I call "cognitively opaque". We can inspect the results, for example by apprehending a feeling of wrongness when we contemplate some act, but the reasons for that judgement aren't accessible to our introspection — the reason we came to that apprehension is computed somewhere below consciousness.

I completely agree with all of this and I like the way you put it together. Morality is best understood biologically/psychologically/culturally. It isn't as though, in the absence of consciously deciding on a moral code we will be without one. Unless we're raised in a closet with minimal contact we will most likely already have a moral sense -unchosen- to be discovered, not decided upon.

There is something about consciously assenting to what we deem moral which is necessary to convey the sense of what we want the word to mean. But it may be that sense of the word carries a naive, mistaken view of human nature.