The study of modern-day mass killing is arguably incomplete without an account of whether and how mass persuasion plays a role. There are at least two key theoretical arguments for why mass persuasion is central to a deeper understanding of how mass killing comes about. First, for perpetrators' potential participation in, and execution of, mass killing, the calculus of their costs and benefits will be shaped by their beliefs, which in turn are formed, in part, by mass media exposure. Direct persuasion due to mass media exposure may increase hatred 
of, and violence against, perceived enemies. Just as marketing campaigns can convince people to buy products or services of a certain brand, and just as political campaigns can convince people that a certain political candidate is worth voting for, mass media, in principle, can convince people to participate in mass violence. Second, indirect …