If you think that buying diamond is an ethical dilemma, read this Foreign Policy article about the ethical issues of several common products.
Take for example, chocolate:
Beware of: Cocoa powder
The cost: Child labor. Seventy percent of the world’s cocoa (and most of the United States’) comes from West Africa, where nearly 300,000 children under the age of 14 toil in dangerous conditions on cocoa plantations. In the Ivory Coast, where more than half of the region’s cocoa is produced, more than 100,000 children work in near slavery, subject to both injury from the machetes used to harvest the plant and from toxic pesticides that are banned in the United States and Europe.