That is fair. (And a pithy statement of the problem!) But Eternal September isn't the only failure mode here. There's also the problem of encouraging diversity of opinion. The ideal community is neither too open nor too closed. It has ways to discover new interesting voices, and ways to focus on existing interesting voices. Following a tag + ignoring users is currently too blunt, yes, but we don't have to give up on it just yet. Some ideas: ranking posts on tag pages (which we already do but can improve), filtering posts that lots of people choose to ignore, permitting whitelists on some (broad) tags and blacklists on other (narrower) ones. Now a private group of people that all know each other can be great in spite of being closed. But it's incorrect IMO to extrapolate that all closed groups are close to optimal.