I think you might be able to find some good opposition to this idea in Kant's Categorical Imperative. I learned it a while ago but I can try to summarize it. Basically, when looking for moral laws or "rules" he says that you should never act in a way that you wouldn't wish to become a universal law. When you look at it that way, some moral standards come about naturally in my opinion. For example, we shouldn't kill each other because in a world where killing was morally allowed, we as humans wouldn't be able to flourish. There were times in the past when this was the case; when we killed anyone who was opposed to us and brute power became the law of the land. I don't think that kind of world, however "natural", is better or more virtuous. There definitely are some immoral opportunities that are possible uniquely because of civilization but the same applies to the "natural world" and animals.