Resources or assets have value. And assets either exist or they don't. Debt behind fiat currencies factually exists - every unit of fiat currency is issued as loan or bond.
There's no evidence to confirm the existence of this debt. Consider the scenario where a government arbitrarily prints a trillion dollars without any underlying assets or value creation. This action merely steals purchasing power from the general populace. It does not create value.
So, faith has nothing to do with assets.
Indeed, it does have. The authority over currency issuance lies with the government. Therefore, regarding fiat currency as a reliable asset is essentially based on faith, as the government retains the power to render it valueless at its discretion, with or without existing debt.
Wait, what? There's no evidence? It is common knowledge that units of fiat currencies are created by banks issues loans and purchasing government bonds. Did you live under a rock all the time?