You’re also, like other commenters, unnecessarily stuck on the example of gold. See past that. Gold is no different from any other object—anything can lose its value, because that value is the product of human activity, ideas, and relations in a market. When I say If everyone decides gold has no value tomorrow, it has no value, I was talking all value. Your scheme won’t work when everyone decides gold has no value, because gold is nothing more than an object in the market whose value is constructed by human relations and activity.
Think about diamonds. They have utility to and they have value as jewelry, they used to be of almost no value as jewelry.
It's not impossible that we will be able to create to find another metal that corrosion resistant. The value as a jewelry is exactly like bitcoin. It's speculative.
And then I will buy the entire supply of gold and abuse my market power to force manufacturers to pay exorbitant prices and become a billionaire.
Why? Because even if all the speculators have left people still want jewelry and corrosion resistant metals.