[upofadown]

No one really wants their legal identity linked to a messaging identity anyway. It just isn't a suitable concept. Identity in a messaging context normally has multiple instances. You don't want your work identity linked to your family identity linked to your bar identity...

Leaving off the question of how useful the transitive stuff is, PGP has a reasonable and simple framework. The terminology of key trust is terrible though. Few people know what it means to trust a key (my house key is OK but I think my shed key might be up to no good).

Messaging identity reputation is all about what you think of the other people's identities. Do you know them? What context do you know them from (e.g. a particular protest)? Why you think this messaging identity relates to a person somehow? How is this entity allowed to interact with you? This stuff can't be automated away.

I think the ultimate answer would have to involve generating a simple conceptual model of a messaging identity and then teaching people about it. If you solve identity then everything else is easy.