The equivalent to your analogy is the "My Pictures" folder we all have on our private computers. Google is not this. They are a giant corporation letting you store your photos with them for free and they have documented that tagging is sharing.
Google's whole goal for G+ is that it's supposed to be modeled after how life really works – circles, hangouts, etc. The picture sharing is not how things go down in the real world. When your aunt has goofy pictures of you at family gatherings, chances are she's showed them to a handful of other individuals without your consent. The pictures are hers and she shares them with her circles, regardless of who's present in those photos. The way Google is handling this seems to go against the ethos of G+.
Actually, before Google+ existed Picasa supported the ability to tag people in photos, and manage albums with limited/restricted sharing. So this is a fundamental change to functionality.
