The first part of the essay highlights the importance of ethical issues at the basis of the mass consent to Nazism and the key role of the medical corporation in supporting the legitimacy of the extermination. Also from this point of view the Aktion T4 represented the first act of the «final solution». The centrality of moral questions in the history of Nazi crimes however poses a problem: if the regime generated a new «ethic of extermination», how to evaluate today the conduct of Nazi doctors and those who assisted them? The paradox could arise that we would condemn as criminals those who slaughtered in good faith to prevent contagions and degenerative processes. The aim of the essay is to show that the «transvaluation of values» hoped for by the regime did not take place and the massacres were carried out in the awareness of their criminal character.