Facebook forgets that there'e something just a little bit sacred about an inbox.

Facebook has announced a new method of money-making: "a small experiment to test the usefulness of economic signals." The experiment will allow users to send messages to people they are not Facebook friends with for a small transaction fee. Think LinkedIn Premium's "InMails" system.

As All Things D's Peter Kafka explains it:

A limited number of U.S. Facebook users will now have the ability to pay Facebook a fee to send a message other U.S. Facebook users who they don't know. Facebook isn't spelling out the cost publicly, but people familiar with the company's plans say it will start at a dollar a message, and will tinker with the fee over time. The option will only be available to individual users -- not marketers and brands -- and Facebook will only allow users to receive a single paid message per week. But users can't opt not to receive paid messages.

Now, Facebook's take on this is slightly different: The service emphasizes the fact that pay-to-say-hey is essentially Facebook's way of stepping in where "social and algorithmic signals" fall short. Basically, when Facebook's existing, friend-based infrastructure falls short. So, for example, if you're a fan of Neil deGrasse Tyson (and who, indeed, is not a fan of Neil deGrasse Tyson?) ... and if Neil deGrasse Tyson is not, in turn, a fan of you ... then you can pony up a buck to send him a note. Or if you want to ask someone about a job opportunity, Facebook notes -- or ask a question of someone you heard speak at an event -- all it takes is a dollar. 

The idea here is that social connection in the broad sense does not need to rely on social connection in the narrow. Gone are the days when we needed formal "notes of introduction" to be connected to people whose acquaintances we want to make. Gone are the days, too, when we needed to be networked with people in order to communicate with them. Now, for the price of maybe-a-dollar, Facebook will act as your social secretary. The benefits of this to the desirer of acquaintance, Facebook suggests, are so obvious as to be implied. For the receiver, the benefits are less obvious -- though this method, Facebook points out, "allows them to hear from people who have an important message to send them."

So. On the one hand, this is a legitimately interesting monetization experiment -- and, for that matter, a legitimately interesting social experiment. Will people actually want to be connected in this money-moderated way? How will the introduction of money to the workings of introduction itself -- the "economic signals" Facebook mentions -- change those workings' dynamics? The system could have a nice deterrent effect, Facebook points out, discouraging spammers (who ostensibly wouldn't be so willing to pay to play) from reaching your inbox. 

On the other hand, though, this experiment is also a slippery slope to another kind of violation -- not so much of user privacy as of user private-ness. Of people's ability to determine the environments that surround them as they go about their days online. Facebook is, by default, a very public place. But it is also varied in its publicness: In its ecosystem, there are some spaces that are meant to be seen by everyone, and some that are meant to be seen only by you; some that are meant to be highly serendipitous, and some that are meant to be highly controlled. The private message box, in theory, occupies the upper-right corner -- the most controlled and the most private area -- of that matrix.

And in that, importantly, it follows a logic established by the rest of the Internet, a long time ago: the assumption that there is something just a little bit sacred about an inbox. Even the word -- in, box -- suggests containment, separateness, a sense of not-yours-but-mine-ness. The inbox is not only a kind of highly personalized publication; is also in some sense the ultimate social network, curated largely and implicitly by connections one has chosen for oneself. There are exceptions to this, as the sea of spam in my own inbox will attest. But the logic remains: My messages are for me and of me and by me, even when they occasionally include notes from Nigerian princes.

That logic, you would think, would hold especially true for Facebook's inbox. Because on Facebook, that community where so much is public, the private takes on an even higher value. There, the implications of the private message -- inbox as place, inbox as network -- matter even more. Users carry the curatorial logic of email to Facebook. And they take that logic one step further, believing that the messages they receive will come only from people they know -- believing that they'll see notes from Nigerian princes only if those Nigerian princes are also their Facebook friends. Only, that is, if they're already connected. They believe that because it is the logical thing to believe, but they believe it as well because it is what Facebook has told them all along. Whatever the worth of this latest "small experiment," to Facebook or to anyone else, it's another reminder that what Facebook thinks of as "evolution" often means, for its users, disruption -- of expectation, of trust, of the environment they'd adapted to.