with modern synthetic diamond processes, couldn't enough Koh-O-Noor Diamonds be produced to keep everyone happy?
Like you could buy a $15 Casio wrist watch and it will tell you time just fine, but if you buy a Rolex you aren't exactly paying for time keeping. The value here is not time or time keeping, it is meant to show the wages and expenses of people/resources taken to produce it up the chain.
It took X slaves to produce this.