The reasons fiat currency has value are far more complicated than just "taxes". If that were true, people would only convert their money to dollars as needed to

The reasons fiat currency has value are far more complicated than just "taxes". If that were true, people would only convert their money to dollars as needed to pay tax, but obviously that's not the case. There is an inherent value to a currency system, and that value amplified by network effects. The government definitely anchors that network (through many mechanisms, not just taxation), but there's still a lot of inertia there regardless.