I'm the kind of nerd that still plays pen and paper dnd. I play on a minecraft server. I'm in a lisp usergroup. The groups have nothing in common, and nothing to do with real life. I've found circles handy.
I think the complaint is that you don't actually care whether someone from your lisp usergroup actively wanted to see your minecraft posts. For security its the publisher who wants categorization of others, but for avoiding categorical issues it is really the consumer who wants to be deciding what they want to see.
After thinking about it for a while, i think this subscriber chooses pushes you back into the undershareing problem. Since there's no way for me to tag intentions of posts, there is no way for subscribers to filter out me prattling on about minecraft.
Furthermore, if they have to go through all that effort to set up circles and then filters based on content, why not just unsubscribe?
I understand it feels like you want to see everything from everyone, but then i'm not going to say anything, because my messages must be carefully crafted for a broad audience. The more I can narrow the communication targets, the more information i can cram in a message with jargon, acronyms, and silly examples in groups of three.