It's a pretty ugly history of colonialism, slavery and genocide going back even before the modern blood diamond issues. Things have greatly improved in the last twenty years, but the Kimberly Process (the means by which dealers certify their diamonds are non-conflict) is so flawed by corruption within diamond producing nations that human rights groups claim there's no way of estimating what percentage of "conflict-free" diamonds are still blood diamonds. Some groups say it's pretty high, but even if the number is low, that's still people dying over diamonds. Besides which, diamonds are kept artificially valuable far beyond their actual rarity through means of market manipulation, so theoretically, even the purchase of legitimately conflict-free diamonds still contributes to the existence of a blood diamond market, especially through the increased sales of uncertified diamonds over the internet. Sucks, right? It's a lot like the way that the popularity of artificial and antique furs still perpetuates a smaller, but nonetheless real and thriving fur trade, only with human lives instead of baby seals and farmed minks.