“It never happened and besides they deserved it.” The title of Edward Opton's (1971) article on responses to the My Lai massacre succinctly captures the acute psychological discomfort that his respondents felt when presented with graphic evidence of the atrocities US soldiers had committed in that unfortunate Vietnamese village. Their simultaneous desire both to deny and justify what their own countrymen had done has no cognitive logic but does have an emotional constancy – the reluctance to believe that their own troops had committed such terrible acts.

War – despite the manifest immoralities it typically brings – is a moral commitment, and evidence of immorality by one's own side undermines that commitment. Public support for war is usually premised on the idea that the threat is so terrible and so imminent that waging war is a lesser evil than letting the enemy triumph, that the current loss of life will prevent larger tragedies later (see Bellamy, this volume, about a related point concerning torture). And yet, as the responses to My Lai show, this moral calculus does not rest on a dispassionate dissection of evidence. So we need to probe the dynamics of the emotions and perceptions that accompany the moral decision making.

The fusion of affective and cognitive dynamics in the support for war was insightfully explored in the work of a pioneering psychologist in this area, Ralph K. White.