Why can money be used as money? Simply put, it can be exchanged freely.

The underlying logic of this matter is actually supported by privacy.

Why do fiat currency and gold have global hard currency status? It's because they can be perfectly exchanged—there's no difference between this hundred-dollar bill and that hundred-dollar bill, and this piece of gold is worth exactly the same as that piece of gold. No one will check your wallet to see "who the previous owner of this money was."

The premise of circulation is anonymity; only with anonymity can there be substitutability. Once every transaction is tracked and traced, funds will no longer be a pure symbol of value; they will carry history, tags, and discrimination.

This is also the core proposition that certain privacy coins have been emphasizing: true currency needs to protect the privacy rights during the circulation process.