Drummond, you say:
“[Concrete identifiers such as an email address] reveal a direct method of interacting with me (as would a phone number, fax number, IM address, postal address, etc.)”
This is an argument you also made in the First Corollary. I want to point out that my i-name [XRI] is also a direct method of interacting with me. BUT, I maintain control of the channels of communication so I don’t have to be protective of it.
I give out my home address (fairly) freely because I trust the security (my dog) to help me manage and maintain control of ingress and egress, much as I trust my authentication service and related communications service providers.
Andy is correct — I keep referring as XRIs as abstract identifiers that do not reveal a direct method of interaction with the resource they represent, particularly when the resource is a person who wishes to keep those methods of interaction private. Andy’s point is that XRI resolution CAN provide such a direct interaction method (such as i-name contact pages), but that due to the additional level of indirection, the XRI authority can control the use of this method of interaction.
Net net: XRIs for people can provide the best of both worlds – direct interaction and privacy protection.