Ethics emerged as a frequent debate among researchers and physicians in the early twenty century. Physicians who were part of the Progressive Era reformers could be found guilty of using “unethical experimentation” under the premise of “experiments [being] necessary to advance medical knowledge.” The individuals frequently used for such experiments were children, the mentally ill, and impoverished peoples. Mentally disabled individuals were “perfect” test subjects for pathogens; gonorrhea research was reliant upon these individuals in the early 1900s. Not only that, but radioactive experiments were tested using disabled children. (This was mid-century, so the trend continued.) Unethical experiments and treatments relied upon the abuse of mentally disabled or ill individuals. It was questioned to “what point does neurotic become unable to give consent?” This was, of course, pushed aside in the earlier 1900s and caregivers (if still present) were shielded from the hours of experiments.

Regarding general acceptance, many of these experiments were hidden. Parents were told their children were at camps or on vacation if individuals were still with their families. People with mental disorders were “wards of the state” and treated as if they were a “growing burden.” survivors of mental institutions remark that “people went into treatment but never came back." For more information on the second part of your question, I encourage you to look into eugenics in the United States. The impact of eugenics on mentally disabled/ill peoples was horrific and very much so in the public face until the mental ill were shoved out of public sight. 

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Lederer, Susan. "Experimentation on Human Beings." OAH Magazine of History 19, no. 5 (2005): 20-22. http://www.jstor.org.proxybz.lib.montana.edu/stable/25161974.

Lasagna, Louis. "Special Subjects in Human Experimentation." Daedalus 98, no. 2 (1969): 449-62. http://www.jstor.org.proxybz.lib.montana.edu/stable/20023886.

Adil E. Shamoo, David B. Resnik, Responsible Conduct of Research, pg. 238, 2015.

United States. 1986. American nuclear guinea pigs: three decades of radiation experiments on U.S. citizens: report. Washington: U.S. G.P.O.

Cold Spring Harbor Laboratory's Image Archive on the American Eugenics Movement, Topic: Mental Illness