I like this. That sounds like a really interesting book.
Well, first, as an opponent of hunting for sport, I would take issue with anyone shooting an animal.
Your argument seems to be rooted in the supposition that the life of an animal is not as important as that of a human being. I, who, even as a religious child, was always taught that human beings are a kind of animal, see no reason why that should make their lives less valuable. I see it as an unfortunate side-affect of the belief in Creationism, that some people view human beings as vastly superior to other kinds of animals, and therefore, when introduced to the idea that humans are also animals, are offended based on their belief that "animal" is an inherently negative term. If all living creatures are animals, then animals can't be "worse" than another form of creature, can they, being that there's only one? Unless you choose to believe that plants are superior to us.
But, secondly, I have to return to the point that has been made time and again in this thread: Why should the hypothetical truth of evolution/falseness of God negate the the importance of moral action? I understand, I think, the point that you're trying to make; that if morality is a God-given trait, and violence is a natural, or animalistic, trait, then the removal of God should leave no argument against our naturally violent tendencies. I would point out a common flaw of such reasoning, as I suggested earlier: you attribute morality and other "civilized" traits to religion alone, and assume that those who don't credit God with giving them to us would also reject the ideas themselves. Well, there are certainly *violent and cruel people on this earth who like to reject them to excuse their actions, but most people, religious or not, don't. I think that moral ideas are inherent to the human brain, then got attributed to God with the advent of religion. People who don't believe in God still believe in acting morally (*with the noted exceptions, which occur within the religious population as well). Being an animal doesn't mean being stupid. Human beings are intelligent, emotional animals, with an advanced notion of how to keep peace within their social circles, which often involves suppressing our more primative violent tendencies. Not shooting each other isn't a religious idea; it's a human idea. Although, there is mounting evidence that we may not be alone in that:
An old BBC article addressing animal sentience
A cool, cool website about animal sentience
A Cool Social Morality Quiz