Common Actions Normalize Inequality in Third-party Morality

Third-party morality plays a central role in regulating social life, yet the psychological principles guiding such judgments remain unclear. Third parties often hold two separate motivations: Judging outcomes as unfair (‘inequality aversion’) and judging actions as normal (the ‘common-is-moral’ heuristic). This can lead to conflicts, such as when a common action results in unfairness, raising the question of how both motivations jointly shape moral judgments. Across three experiments (N = 905), we examined this interplay by systematically manipulating an action’s commonness and the inequality it generated. In Study 1, we evaluated two minimal tasks which successfully captured inequality aversion and the common-is-moral heuristic. To investigate the interaction between both moral motivations, we combined the two Study 1 tasks into a novel paradigm: Study 2 revealed simultaneous effects of inequality aversion and the common-is-moral heuristic, and, crucially, demonstrated an interaction between the two. Common actions reduced sensitivity to inequality, such that identical payoff differences were judged less harshly when they resulted from frequent rather than rare behaviors. Study 3 replicated this pattern and showed that punishment intentions followed the same trajectory as moral judgments, highlighting that widespread actions dampen the moral condemnation of unfairness. We employed agent-based simulations to investigate the broader social consequences of this interaction. While inequality aversion promoted collective welfare and the common-is-moral effect stabilized cooperation, their interaction frequently undermined welfare by normalizing unequal outcomes. Together, these findings identify a mechanism through which the status quo can suppress fairness concerns and entrench societal inequality.