I think our grouping of friends is generally suppressed in our thinking. We have fine-grained distinctions among our friends, but we generally don't see it that way because they're not important re friendship.

Instead, we have different conversations with different friends. While this is normally private, that's only because of how we're interacting--in person, over chat, etc.--and not because of any desire to keep it secret. A social media site has analogs to a more general meet-up or party in that our conversations are often on the side: we're not talking to everyone but we don't mind people listening in.

The article's critique wouldn't have much intuitive appeal if it was possible to create "open" circles where conversations wouldn't appear in public, but a user who wished to see them could listen in and possibly comment, signaling their interest in joining that group.