Appiah uses a list of taboos to show that all humans find something disgusting because it has been an evolutionary force throughout history. Even when normal chocolate is "shaped like dog feces" we will not eat it. In addition, people find different things disgusting because of their culture. I think he describes a variety of disgusting things in order to relate to many different cultures and audiences. This excerpt also shows the power of a culture. Even when eating cats does not cause any danger, many cultures still refuse to take part in the act. I think the purpose of the passage is to show that all cultures are different but not deficient.