Clinical evidence demonstrates that killing among soldiers at war predicts their experience of long-lasting trauma/distress. Killing leads to distress, in part, due to guilt experienced from violating moral standards. Because social consensus shapes what actions are perceived as moral and just, we hypothesized that social validation for killing would reduce guilt, whereas social invalidation would exacerbate it. To examine this possibility in a laboratory setting, participants were led to kill bugs in an "extermination task." Perceptions of social validation/invalidation were manipulated through the supposed actions of a confederate (Study 1) or numerous previous participants (Study 2) that agreed or refused to kill bugs. Distress measures focused on trauma-related guilt. Higher levels of distress were observed when individuals perceived their actions as invalidated as opposed to when they perceived their actions as socially validated. Implications for posttraumatic stress disorder (PTSD) experienced by soldiers and the paradoxical nature of publicly expressing antiwar sentiments are discussed.