An important observation: defining the notion of "identity" as a construct is functionally identical to establishing a locus of authority.

True of any mechanism of power, of course, but insisting that identities be unique means the auditor or enforcer of that uniqueness has been granted a position of specific power. For example, if your drivers' license or passport is the guarantor of identity, then the function of anonymity is reserved to the state, that can print whatever docs it wants.