Who wrote the story? God or man? The general consensus is that these stories, while inspired by God were written by man as a way to present life lessons. Knowing God is, I've always been quizzical (but accepting) about how some so easily dismiss him. People of faith are to be both admired and maybe even envied.
Let's address your 'Maybe'...that there is no God. Is there goodness and is there love? Do you go on to submit, there is no goodness and there is no love--both are human constructs? Or, can we consider the possibility that Goodness, Love, and God have always been a part of human life and were (correctly) identified, very early on by early man?
Consider if the story of the Great Flood began with: Wickedness, introduced by man, was encroaching upon all the Goodness in the world...A great flood washed away all of mankind accept for one good family...When the flood ended this good family began anew...
Since this was a story told years, centuries after the flood, when people again saw sprouts of wickedness sprouting in their midst, specifically, of what particular wickedness was the story warning the people? (To address your point of killing animals, the story specifically notes that this was not wrong or wicked.) So....What was causing wickedness to reinsert itself into society?