The Twittersphere is up in arms over a move the message-broadcasting service made to make its site a bit less noisy: You can no longer easily eavesdrop on conversations with strangers. Hurrah!

Technically, Twitter has stopped displaying what the site's power users call "@replies" — messages broadcast in public, but directed at a specific user — when the viewer doesn't also follow the message's target. Twitter users will still see conversations, but only when they happen entirely within their social circle.

For the attention-deficited social butterflies of Silicon Valley, this is a horrible development: They can no longer ignore their existing friends in favor of constantly finding new ones.

But for the mass market Twitter hopes to tap, this is a great thing. New users find Twitter overwhelming and confusing; some 60 percent drop out after signing up, according to Nielsen, which means Twitter is proving far less capable of retaining an audience than Facebook or MySpace. These Twitter quitters mean that Twitter's growth lies on the edge of a knife. While its traffic numbers are growing at an unheard-of pace, it could lose its audience all too easily.

Social networks always go through a boom followed by a plateau. The trick is to sell out while the growth curve is at its highest. Friendster committed market suicide; MySpace sold far too early, for $580 million; Facebook may have squeezed $240 million out of Microsoft, but many believe it missed its chance for a bigger payday. The risk for Twitter: that it becomes one of those places that's so popular no one goes there anymore.

Twitter's noisiest users are complaining about the change, claiming that it's taken away from Twitter's "conversations." What they're missing: The absence of non-sequitur @replies has made Twitter a far more comprehensible place, especially for the newbies they claim they'd like to talk to.

There's an obvious answer for Twitter's hardcore nerd fanbase, as well as the businesses that have flocked to Twitter to monitor their most passive-aggressive customers' whiny complaints in real-time. Twitter should start charging to let an account broadcast its @replies to everyone. Twitter can make money. Businesses can advertise how responsive their Twitter customer service is through their replies. And people hellbent on talking to strangers can pay for the privilege. Meanwhile, the rest of us will get a place to talk that's not filled with people shouting at strangers. If we wanted that, we'd go to the local park.