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In 1999, when Scott McNealy, the founder and CEO of Sun Microsystems, declared, “You have zero privacy…get over it,” most of us, still new to the World Wide Web, had no idea what he meant. Eleven years later, when Mark Zuckerberg said that “the social norms” of privacy had “evolved” because “people [had] really gotten comfortable not only sharing more information and different kinds, but more openly and with more people,” his words expressed what was becoming a common Silicon Valley trope: privacy was obsolete.

By then, Zuckerberg’s invention, Facebook, had 500 million users, was growing 4.5 percent a month, and had recently surpassed its rival, MySpace. Twitter had overcome skepticism that people would be interested in a zippy parade of 140-character posts; at the end of 2010 it had 54 million active users. (It now has 336 million.) YouTube was in its fifth year, the micro-blogging platform Tumblr was into its third, and Instagram had just been created. Social media, which encouraged and relied on people to share their thoughts, passions, interests, and images, making them the Web’s content providers, were ascendant.

Users found it empowering to bypass, and even supersede, the traditional gatekeepers of information and culture. The social Web appeared to bring to fruition the early promise of the Internet: that it would democratize the creation and dissemination of knowledge. If, in the process, individuals were uploading photos of drunken parties, and discussing their sexual fetishes, and pulling back the curtain on all sorts of previously hidden personal behaviors, wasn’t that liberating, too? How could anyone argue that privacy had been invaded or compromised or effaced when these revelations were voluntary?

The short answer is that they couldn’t. And they didn’t. Users, who in the early days of social media were predominantly young, were largely guileless and unconcerned about privacy. In a survey of sixty-four of her students at Rochester Institute of Technology in 2006, Susan Barnes found that they “wanted to keep information private, but did not seem to realize that Facebook is a public space.” When a random sample of young people was asked in 2007 by researchers from the Pew Research Center if “they had any concerns about publicly posted photos, most…said they were not worried about risks to their privacy.” (This was largely before Facebook and other tech companies began tracking and monetizing one’s every move on- and offline.)

In retrospect, the tendencies toward disclosure and prurience online should not have been surprising. As Sarah Igo observes in The Known Citizen, her masterful study of privacy in the United States, the sharing and oversharing of intimacies predates the social Web; indeed, the social Web simply allowed these behaviors to proliferate on a more open and accessible platform. Igo cites the enormous popularity of An American…