While it's true that the value of an asset can be based on its usefulness, it's important to note that usefulness is not the only factor that determines the value of an asset. Scarcity, demand, and perceived value also play a significant role in setting market prices.

Bitcoin has several use cases beyond just trading and buying with fiat. For example, it can be used as a medium of exchange for peer-to-peer transactions without the need for intermediaries, as a hedge against inflation and political instability, and as a way to store wealth outside of the traditional banking system.

Additionally, Bitcoin has several technological advantages over traditional currencies, such as its decentralized nature, its ability to facilitate cross-border transactions without the need for conversion, and its low transaction fees.

While the US dollar has the advantage of being legal tender and used to pay taxes, it's important to recognize that the value of the dollar is subject to inflation and government intervention, which can erode its purchasing power over time.

As for gold, while it does have industrial uses, it's important to note that its value as a store of wealth has historically been based on its scarcity and perceived value, rather than its usefulness. People have valued gold for centuries as a symbol of wealth and power, and this perception has helped to drive its price.