Americans believe that deviant political ideas can influence other Americans’ thoughts and actions because many people can express a wide range of ideas via social media. In response, Americans are less tolerant of political expression in the hopes that restricting political expression will decrease the potential influence of deviant political ideas. I find moderate support for this thesis across four studies. The Perceptions of Mass Media Study and Perceived Influence Study show that Americans believe deviant political ideas are influential because many people can express a wide range of ideas via social media. The Contexts of Expression Experiment finds that Americans are less tolerant of political expression via social media relative to the same expression face-to-face. Finally, the Perceptions of Social Media experiment provides causal evidence that Americans are less tolerant of political expression due to the belief that deviant ideas can be influential via social media. These findings make three contributions. First, these results highlight the role media play in political tolerance. Widespread expression via media was not possible prior to social media, so prior research overlooks variation in tolerance arising from different media of expression. These results suggest that future research ought to account for this variation. Second, prior scholars have identified widespread moral panics following the development of new media technologies stretching back to the printing press (e.g. Marvin 1988; Orben 2020), but this is the first project to empirically document public beliefs about a new medium and the outcome of these beliefs on concepts of interest to political scientists. Third, liberal democracy ought to be invigorated when more people can express a wider range of ideas into the public sphere, yet Americans believe deviant political ideas that harm liberal democracy spread because many people express a wide range of ideas via social media. As a result, Americans want to restrict political expression, contradictory to liberal democratic norms.