The law often calls on the concept of public interest for assistance. Privacy law makes use of this concept in several ways, including to justify consent waivers for secondary research on health information. Because the law sees information privacy as a means for individuals to control their personal information, consent can only be set aside in special circumstances. Ballantyne and Schaefer argue that only public interest, and only a broad conception of public interest, can do the special ‘normative justificatory work’ to override consent requirements. Other, similar-sounding concepts, such as public benefit, public good and social value, also provide useful services. But none more so than public interest. In fact, they argue, public interest is the superior concept precisely because it can capture those concepts as well as a range of other interests. Our response focuses on this claim. We argue their strategy is not as promising as it might first seem. Ballantyne and Schaefer construe the important role that public interest plays in this context as their endpoint. They claim that unless the concept is open and content-rich, it will lose some of its importance. But by refusing to place limits around it, their inquiry leads us back to a catch-all concept that lacks clear focus or meaning. In reply, we argue that, for practically minded theorists, a narrow conception of public interest is more useful. Further, the narrowing of public interest in this context can be achieved by first analysing it in its legal, rather than ethical, sense.