How can we make moral progress on factory farming? Part of the answer lies in human moral psychology. Meat consumption remains high, despite increased awareness of its negative impact on animal welfare. Weakness of will is part of the explanation: acceptance of the ethical arguments doesn’t always motivate changes in dietary habits. However, we draw on scientific evidence to argue that many consumers aren’t fully convinced that they morally ought to reduce their meat consumption. We then identify two key psychological mechanisms—motivated reasoning and social proof—that lead people to resist the ethical reasons. Finally, we show how to harness these psychological mechanisms to encourage reductions in meat consumption. A central lesson for moral progress generally is that durable social change requires socially-embedded reasoning.