This article compares theories and social policies of social democrats and other representatives of the left-wing political spectrum in six European countries to explain why, in certain countries such as Sweden, Norway, and Switzerland, weak social groups became the target of illiberal and negative eugenic policy, especially isolation and sterilization, while elsewhere left-wing politicians and theorists were far less radical. One striking feature that emerges is the difference between a communitarian-organic and a class-bound form of socialism. Following Zygmunt Bauman, Michel Foucault, and James C. Scott, the article discerns a first variant of citizenship that is conditional and intended only for those with the right social attitude. Eugenics was perfectly consistent with such a view, since it offered a diagnosis and at the same time a cure. Prominent representatives of this approach were the Webbs in Britain and the Myrdals in Sweden. Such an organic-medical approach was less likely, however, in a more class-dependent variant of socialism embedded in a strong civil society. As long as social democrats and other leftist politicians believed social problems such as inequality and poverty were caused primarily by an unjust capitalist system, there was little cause for a eugenicist solution.