In the early 1900s, a psychologist named Henry Goddard developed a school of thought for segregating mental patients he referred to as "feeble-minded" into special institutions. He based this on a patient of his that he named "Deborah Kallikak," and a very flawed study into her family history, which became the basis for the 20th Century practice of eugenics, classifications of mental patients, and forced sterilization of patients. "Deborah's" real name was Emma Wolverton, and David Macdonald discusses her family history as twisted by Goddard at length in his book. Goddard theorized that "mental deficiency" was hereditary, and therefore the way to treat it was to prevent those who were categorized as such from procreating. He later recanted at least part of his theory, but not before it became an extremely popular basis for stigmatizing mental illness and poverty, both in North America and in Europe (especially in the U.S. and Germany). Thankfully most of this has since been discredited. Goddard's book and the distorted picture it paints of mental illness and poverty can be ready here.
J. David Smith and Michael L. Wehmeyer have published a very strong online refutation of Goddard's pseudoscience called Who Was Deborah Kallikak? Another good explanation is provided in The Wolverton/Kallikaks by Jon K. Shidler.