You: Here's a distasteful counterexample.

The hookworm is a parasitic creature that enters a human host through the feet, makes its way to the lungs, down the throat and into the intestines where it hangs on for dear life drinking blood and laying thousands of eggs for the rest of its days.

As you can see, the complex life cycle of the hookworm depends completely on the existence of human beings. They could not live without us, although we would be happy to be without them. Does this imply to you that people were created for the express purpose of supporting hookworms.

Aaron: That is just a more extreme example. Again, the system you describe has no useful purpose.

You: It may not have much use for us, but it is quite convenient for the hookworm.

Aaron: No. Hookworms are unthinking and incapable of truly benefitting from anything. Such parasites are meant to make man uncomfortable and tempt him into sin. This is part of God's plan, and I know that you will not let me say anything about God's plan until I have proven to you that God exists, so let me move to a subject that will be more to your liking.