It's like people who insist on "real names" and "one true account" don't get that people specialize. It's not about anonymity or not being accountable for stuff, it's about having a signifier that this identity interacts with these people and places in this way. It's the reason that well-known authors who want to jump genres will use a different name -- to make it clear that they're engaging with a new audience.

I think Google has the weird idea that their innovative, totally unique, not seen anywhere before on the Internet "circles" (ow, I hurt myself with my own sarcasm) gives people enough ability to specialize, so that they can simply add everyone at once -- work, parents' groups, church, family, friends, acquaintances -- and use the circles to create those boundaries. But most Internet-savvy people have already created our own boundaries, and it would be nice to have those boundaries respected and accounted for.