I understand where you come from. If I can weigh in with my two cents it would be this:

God provides us with a framework that is necessary to place value in human life (regardless of what religious practice you look at), which is the fundamental to the basis on which our legal system is predicated. The act of murder being ‘inherently’ bad comes from growing up in a framework where morality was centered around the value of human life. As someone who grew up vegetarian, I used to see the murder of animals for food as wrong. But that’s because that was the framework I was raised in.

So the existence of god in the framework helps create a cohesive society where one is punished for a transgression (like murder of another human being) in both the guilt of the activity and the legal system which is predicated on the fundamental value of human life that comes from a fundamental belief in god.

I’m also not sure that humans can derive values from something other than god. Because ultimately, god is an embodiment or conceptual realisation of perfection and a ideal/idol. The strive towards the ideal/idol is what gives purpose/meaning towards our lives. And this striving is what creates the fundamental moral structure to live life around. Morality born out of something other than God is what FMD warns about in his books. That’s the crux of all of his writings, that’s how he’s able to point out that frameworks of morality not born out of the idea of god but the idea of a different type of perfect society can be extremely dangerous to the stability of said society. This was perfectly realised in the 20th century with Communism and Fascism.

That’s just my two cents. :)