As a modern Christian, the only way for me to look at the Cain and Abel story is as a fictional parable, a device Jesus was quite fond of.

Forgetting the obvious facts behind evolution, the story, if looked upon as historical in any way, is too full of holes to take seriously.

Cain, in asking mercy from God, says, “Whoever finds me will kill me.”

That pretty much leaves mom and dad. Then he goes out and gets married? To whom? Mom? Or one of his later born sisters? Ewww.

Then he builds a city? That’s awfully optimistic in a world with how many people? Six? A dozen? All incest survivors.

I like Isaac Asimov’s take on this, which doesn’t veer far away from yours, that the story is a parable about the nomadic life and the encroachment of civilization upon it.