Eugenicists were particularly interested in mental illnesses, although some were known by different names. Notably, "dementia praecox" we now know as schizophrenia and "mongolian idiocy" is Down syndrome. By the turn of the 20th century, people with mental disorders were usually wards of the state, and eugenicists argued that their care was a growing burden on society. Mental patients made good subjects for eugenic study in state institutions, where eugenics case workers could interview them and obtain their family records. Studies at state mental institutions turned up some of the first "evidence" that "social inadequacy" might be in the genes — some institutions housed a number of related inmates. Harry Laughlin used data from state institutions in his first testimony before the House Committee on Immigration, which purported to show that a disproportionate number of immigrants were insane.
"Feeblemindedness," was considered the most important mental disorder by eugenicists. In addition to abnormal behavior and very low scores on IQ tests, "feeblemindedness" was frequently linked to promiscuity, criminality, and social dependency. Eugenicists feared the "feebleminded," because they could potentially "pass for normal" and reproduce with normal people. This was the case of Martin Kallikak, a normal man who fathered an allegedly corrupt line through his union with an attractive, but "feebleminded" girl.
Feeblemindedness is no longer used in medical terminology or popular language. It was clearly a catch-all term that had virtually no clinical meaning. Many people who were classified as feebleminded would now be called mildly retarded, learning disabled, or simply underachievers. Many were victims of poverty and abuse. The promiscuity shown by some feebleminded would shock relatively few people today and would be within the scope of "normal" sexual activity portrayed on many prime time television shows.
Buck vs. Bell, the Supreme Court case that upheld eugenic sterilization, is a perfect example of the slippery slope of defining feeblemindedness. Both Carrie Buck and her illegitimate infant, Vivian were pronounced feebleminded, and Carrie was ordered to be sterilized as society's protection against her promiscuous behavior. However, in later life Carrie was found to be an avid reader of the daily newspaper and Vivian was a "B" student in elementary school. Vivian's conception had been the result of Carrie's rape, as a teenager, by a relative of her foster parents.