Social networking shouldn't be compulsory, and yet it's becoming an obligation. The hunger among Internet companies for data about who you are, what you do, where you go, and who you know keeps growing. They want you to share so they can earn. So they have violated Communication Neutrality: They have made mechanisms for expression into vehicles for marketing, forcing those who participate in online life to promote.

Social networking has become inescapable. Startups often require a Facebook or Twitter login. Google now requires a Google+ account to post app reviews on Google Play. And in many lines of knowledge work, including journalism, participation in these networks has become a job requirement.

The latest entry in the field comes from Microsoft, which has just opened a social network of its own, the aptly named so.cl. Evidently, the world needs more sharing.

Or it would, if social networks were actually about sharing. The irony of the constant cajoling to share more, of Facebook CEO Mark Zuckerberg's self-serving predictions that everyone will share more in the future, is that social networks themselves limit how they share the data they've collected. They don't so much share as restrict, through contractual API limitations, through incomplete export capabilities, through burdensome processes, under the pretense of user protection, or to spite the competition.

[ Read Facebook Overload: Just Getting Worse. ]

Consider the latest dustup between Instagram and Twitter. According to the New York Times, Instagram's CEO Kevin Systrom acknowledged that his Facebook-owned company has eliminated the ability to embed pictures in Twitter and intends to make posts to Twitter redirect users to Instagram to view images.

Share and share alike? Hardly. You promote, we monetize.

Social networking isn't about sharing. It's about marketing. Perhaps the most obvious proof of that is Facebook's promoted posts, through which advertisers can pay to have their marketing distributed more widely in Facebook users' news feeds.

Sharing at its best is private, personal and genuine. It's direct. It doesn't involve intermediaries. It doesn't have terms of service or privacy policies that describe how you will not be getting privacy. But public sharing is something else entirely. It's publishing, or something like it, paid for by free online services worth far less than the data surrendered and the labor required to produce it. But that's capitalism, isn't it? Buy low, sell high.

Publishing used to imply a separation between editorial and advertising. But these days, editorial and advertising are often blurred in a suspicious slurry. Our reflexive distrust of advertising has been disarmed because the norms of social networking make everything potentially commercial. If you're not promoting someone else's brand, you're promoting the brand that is you. To condemn marketing on the Internet is to be a hypocrite, because everyone's doing it or benefiting from it.

The problem with commercial communication is that it's something less than honest. It's antisocial because it calls trust into question. Social networking undermines the social contract. Marketing might be necessary but it shouldn't pervade every online interaction.

It might be easier to surrender social interaction to intermediaries, but there's no reason it has to be that way. The Internet was supposed to be the great disintermediator. It was supposed to facilitate direct connections between individuals and to disempower middlemen and gatekeepers. Instead, it has become a massive man-in-the-middle attack.

A criminal man-in-the-middle attack is covert and aims to steal important data. A social man-in-the-middle attack is merely obscure and aims to use important data, lawfully though seldom with informed consent and adequate disclosure.

In the years ahead, perhaps it will be different. Despite the underwhelming adoption of social network alternatives such as Diaspora and Tent.io, social networking could become more like WordPress, a service that users could run for themselves through a cloud computing service provider. You shouldn't need Facebook, Google, or Microsoft to share. That's what the Internet is for.