You are half right in theory and almost right in practice. Why? Because many coins are built on two theories. One is consensus as measured and manifested in the network. This is the side most people see and think of when they think of crypto coins. In this world the only thing that matters is opinion/belief. Fiat also runs on a sort of contract/algorithm as Ayn Rand showed in Atlas Shrugged. But most of it is only implicit and is not directly tied to any commodity like gold. The world would see thing more clearly if we still used gold coins. But anyway the other side of crypto is that the contract represents the free will of the individual. Every crypto has a list of standards that is like a bill of rights that it has to confirm to. These are encoded in an increasingly large body of code, when the code reaches a certain level of sophistication then believe me. Fiat will go straight out the window.