The value of a diamond is not its retail value nor its resale value, it's what it means to the recipient. Don't lose sight of the fact that we're here discussing this on the web, where people pay hundreds of dollars for downloads with virtually no marginal cost at all, and markets for unique services consist of a single provider arbitrarily setting prices for something that cannot be resold at all.

If I was going to get angry about diamonds, it'd be about the poor labor conditions of some mining operations, not the artificial value we attach to precious gems. If suppliers allowed diamonds to become worthless, we'd just find some other gift to symbolize what the cost of diamonds symbolize now.