DeBeers having a monopoly isn't really true anymore. DeBeers lost an antitrust lawsuit in 2012 and had already sold off its stockpile by 2004 under increasing pressure for a lot of new mines opening up, particularly in Russia, which wrestled away their control of the market. Prices of diamonds have actually shot up quite a bit since DeBeers lost control but I don't know what the explanation for that is (maybe they were artificially low because of the stockpile selloff?).

I agree that this is a good thing though.