How does group behavior drive extremism and challenge democratic values? Cass R. Sunstein argues that the key to preventing the spread of extremist views is not to suppress deliberation among the like-minded; such groups productively challenge conventional thinking and majority opinion. Instead, policymakers should develop institutions to ensure that like-minded groups encounter a diversity of opinions within civil society. The goal, Sunstein contends, must be to create opportunities for civil deliberation that expose like-minded group members to opposing views, while exposing society at large to the views of such groups.