Edit: this really is the cultural differences thread
In other words: if you don't believe in the supernatural you can't have ethics?
That said, your discomfort is natural. After all, if the foundation of ethics is purely natural, then what is it? Logic perhaps? What logic tells us that murder is wrong, when logically murder is sometimes advantageous? Is it science then? What science tells us that rape is wrong, when evolution tells us fitness is propagating genes? Then is it aesthetics? Are goodness and beauty the same? Or is there an objective standard of right and wrong that isn't dependent on any human being's whims or self-interest? If so, what is its source?
The way you write is suggestive (including the reply you wrote) and that is why I asked for your clarification.