For the past twenty years, the recognition of legal capacity as a human right has given rise to a lively social and scientific controversy concerning the abolition of legal mechanisms for substitute decision-making (forced care, guardianship, curatorship, etc.). Through the development of a participatory research approach, this book examines the emergence of this debate in the international context and its appropriation in France, and explores the tensions between the affirmation of a utopian ideal and its difficult domestication in social life. Far from reducing the language of human rights to an abstract ideology, as is sometimes the case in the social sciences, this book develops an original affirmative sociology combining empirical surveys and a social quest for better consideration of the most vulnerable. In doing so, it sheds light on the anthropological, political and clinical conditions of the advent of an ideal at the same time as its transformative scope.