And what prevents your neighbor from changing the address that the GUID points to? How does USPS or FedEx know that the person trying to edit the GUID's address

And what prevents your neighbor from changing the address that the GUID points to? How does USPS or FedEx know that the person trying to edit the GUID's address is the person who owns the GUID? The reason why it needs to be handled through national ID numbers is because ultimately, national governments are today's identity arbiters, and they do the best job of verifying identity. They're not perfect, but they're the best body for the task, and strong, verifiable identity is the foundation upon which all other security is built.