[WalterBright]

When the Spanish extracted all the silver and gold they could from South America, it caused a dramatic reduction in the value of silver and gold in Europe.

I.e. dropping a huge chunk of rare Earths onto Earth will make them not-so-rare and prices will collapse.

[Super_Jambo]

Only if you don't have a monopoly...

[WalterBright]

You have to sell it to make money.

It's like if Jeff Bezos dumped a big chunk of his Amazon stock on the market. The price would collapse.