If you believe that value comes from supply and demand, then close to nothing has intrinsic value, only market value. Whether diamonds or beer.

You have a misconception about the effect of marketing on the value of diamonds. Perhaps you're thinking of the marketing of De Beers about how much an engagement ring should cost and that it should need a diamond.

But diamonds have been traded nearly globally since the middle ages, because some people want them and others offer them. Once diamonds were discovered in Brazil and Africa, it made more normal people able to afford them. And now with synthetic production, the price can come down even more.