I’m reposting a reply to a non-theist friend on Facebook, where he tried to defend a view of morality without God:
What grounds my morality is the human condition, and that is all that is required to ground it.
But that’s just an assertion that flies in the face of what we know morality is. If moral values have no ontological status [ie no independent existence outside of us], if they are just expressions of our preferences, then to say that it is WRONG to torture children for fun is really just to say that we evolved to have a NEGATIVE REACTION to torturing babies for fun. But that is not morality. A biological impulse is not a moral moral impulse.
Put another way, if that IS what morality actually is, then terms like right and wrong, good and evil don’t have the meanings we ascribe to them. They have no force whatsoever. To say that X is wrong is merely to describe how we feel about it—not to prescribe an obligation regarding it. So you emasculate morality, replacing prescriptive moral terms with descriptive scientific ones, but pretending nothing has happened because you’re still using the same terms. It’s a bait and switch.
Because the human condition is one way, and not another, morals constructed in light of it are not arbitrary.
That only holds if the human condition is not arbitrary. But clearly it is. We can imagine a species evolving to have a positive reaction to torturing babies for fun. In that world, morality is the opposite to ours. So your morality is COMPLETELY arbitrary.
In fact, one of the DEFINING things about morality is that it is teleological. X is wrong because it deviates from the way things are MEANT to be, the way things were DESIGNED to be. But in your view, there is no design. There is no plan. Our evolution was a chance affair, guided by non-rational forces, in a universe where those forces just happen to be the way they are. That’s the very definition of arbitrariness!
They gain their force from the way people are.
Since the way people are is as arbitrary as the way the universe is under a non-theistic view, your morality has no force whatsoever.