Most people seem to agree that individuals have too little privacy, and most proposals to address that problem focus on ways to give those users more information about, and more control over, how information about them is used. Yet in nearly all cases, information subjects are not the parties who make decisions about how information is collected, used, and disseminated; instead, outsiders make unilateral decisions to collect, use, and disseminate information about others. These potential privacy invaders, acting without input from information subjects, are the parties to whom proposals to protect privacy must be directed.
This Article develops a theory of unilateral invasions of privacy rooted in the incentives of potential outside invaders. It first briefly describes the different kinds of information flows that can result in losses of privacy and the private costs and benefits to the participants in these information flows. It argues that in many cases the relevant costs and benefits are those of an outsider deciding whether certain information flows occur. These outside invaders are more likely to act when their own private costs and benefits make particular information flows worthwhile, regardless of the effects on information subjects or on social welfare. And potential privacy invaders are quite sensitive to changes in these costs and benefits, unlike information subjects, for whom transaction costs can overwhelm incentives to make information more or less private.
The Article then turns to privacy regulation, arguing that this unilateral-invasion theory sheds light on how effective privacy regulations should be designed. Effective regulations are those that help match the costs and benefits faced by a potential privacy invader with the costs and benefits to society of a given information flow. Law can help do so by raising or lowering the costs or benefits of a privacy invasion, but only after taking account of other costs and benefits faced by the potential privacy invader.