…given atheism, objective morality probably doesn’t exist—to the point where given atheism, one would be justified in believing objective morality does not exist.
Maverick points out that on atheism, with a different evolutionary origin we could have had a very different set of ethical intuitions. I agree! But so what?
But there are other kinds of facts which are very much like moral facts, and which atheists commonly believe in: epistemic facts. These are facts about what we should believe and what sorts of methodologies we should practice. You shouldn't believe something just because you want to. Rather, you should follow the evidence wherever it leads. These are prescriptive facts very much like the facts of morality. One such epistemic fact I will utilize later on in the debate, sometimes called the principle of credulity, is this: that something appears to be the case is reason in of itself to believe it's so.