Diamonds are a huge scam. They are worth a tiny fraction of what you pay. Every little 5000-person town in the middle of fly-over country has a jewelry store stocked with diamonds but somehow they are rare and precious? Bullshiat. Have you ever tried to SELL a diamond? (new window)

Speaking of scams - the jewelry store that I shop at occasionally has signs all over the store saying "We will never sell lab-created stones". Guess they never read this (new window).

\Or maybe they did, and just don't want anyone else to...

Diamonds themselves are not a scam. It's a lovely, durable decorative gemstone.
It's the prices that are a scam - mostly on the mid range stones.
The small, decorative stones under a quarter carat are reasonably priced for the labor that goes into them (Note: even the computer cut melee they make in Israel require a lot of skilled manual labor).
The really huge stones and the fancies (like the one in TFA) are legitimately rare and valuable.
The rip-off takes place with the mid range stones that are typically sold as engagement rings. A combination of marketing and artificial rarity have inflated those prices well beyond what they would be in a normal market.
The irony is that the movie star who buys his sweetie a 25 carat monstrosoity for a mountain of cash actually gets a better deal than the store clerk who plunks down $1500 for a vs1 3/4 ct. engagement ring. In a world where diamonds were traded and marketed like colored stones are, a decent 1ct. round brilliant would probably go for a couple hundred bucks full retail, if that much.