The killing of people with intellectual disabilities or mental illness was not a National Socialist idea. Even before 1933, there had been discussion on »mercy killing« or »euthanasia« (Greek: good death) with terminally ill people, but also with institutional patients in need of care and newborns with disabilities. The basic principles of this way of thinking were the teachings of eugenics / »racial hygiene« that arose in the 19th century: supporters believed the »genetic health« of a people was at risk of a strong increase in those who deemed »genetically inferior«. Their sterilization and detention in institutions was discussed internationally.

After coming to power in 1933, the National Socialists made eugenics a leading science of their health policy. The centrepiece was the »Law for the Prevention of Genetically Diseased Offspring« that allowed forced sterilization. The propaganda emphasized above all the financial burden caused by »people with hereditary diseases«. This called into question the right to life of people with mental illness and intellectual or physical disabilities.