Whereas most social psychological perspectives assume that needs to manage uncertainty, existential anxiety, and social cohesion should motivate any form of ideological zeal, System Justification Theory predicts that these needs are positively associated with the endorsement of system-justifying beliefs, opinions, and values but negatively associated with the endorsement of system-challenging ideological outcomes. For the first time we test a full theoretical model in which system justification mediates the effects of individual differences in epistemic, existential, and relational needs on attitudes toward public policy issues and social movements. Specifically, we conducted a national survey of 182 Americans and found that, as hypothesized, lower need for cognition, greater death anxiety, and a stronger desire to share reality each contributed significantly and independently to economic system justification, which, in turn, contributed to support for the Tea Party (a movement aimed at restoring America's “traditional values”) and opposition to Occupy Wall Street (a movement seeking to reduce social and economic inequality and minimize corporate influence on government). Economic system justification also mediated the effects of these needs on the endorsement of status quo positions with respect to health care, immigration, global climate change, and the “Ground Zero mosque.” These findings suggest that epistemic, existential, and relational needs lead disproportionately to support for system-justifying, rather than system-challenging, policies and movements.