I guess I got my language wrong here. Maybe what I'm talking about is about portability more than global vs local. Identities should exist at a layer higher than any given social context, and should be "materialized" into that context with local information. It's not about using the same identity everywhere, it's about being able to take the identity where you want to. Similarly it's not about the same information being available everywhere, but information being relative to durable identities, not ephemeral ones.