Okay, maybe it's more like a pyramid scheme. As long as more people keep flocking to it, prices will go up. But you don't know how long people will keep flocking to it.
Under this definition, every currency is a pyramid scheme
pyramid schemes backed by governments with police forces and militaries able to collect taxes in said currency.
Gold and silver were a currency and they weren't backed by government.
That's why I don't trust gold and silver either. They lack inherent value.
It's still gambling, even if it's the opposite of casino games.