As recently as 2010, the idea of legalizing same-sex marriage was all but an anathema in American politics . Yet, by the early 2010s a majority of Americans came to support same-sex marriage, even before the Obergefell v. Hodges decision that ultimately codified its legality. In a similar manner, support for the partial or full legalization of marijuana was once unthinkable, yet many analysts expect the federal government to end its Schedule I status, making it legal across the nation. South Korea, another industrialized democracy, also finds itself confronting these issues. Although there is rising support for same-sex marriage, it has not yet become widely acceptable.
At the same time, whereas Korea has traditionally taken a hard-line stance towards all controlled substances, it recently legalized the medical use of marijuana, a case without precedent in Northeast Asia. These cases raise a couple of important questions. First, how do unthinkable policies, like same-sex marriage and marijuana legalization, become mainstream? What is the social process that causes this to happen? Second, where and why does this fail to happen? What stops once unthinkable policies from being mainstreamed in the public discourse?
In this book project, I argue that unthinkable policies can become mainstream through a number of different mechanisms, but that in advanced industrialized democracies with clear political alternatives, unacceptable policies become acceptable through a dynamic social process driven by political polarization, social norms enforcement, and elite messaging. To support this argument I draw on research based on focus groups, elite interviews, a series of novel survey experiments conducted in South Korea and the United States, and computer simulations.