Why did Republicans enact Eugenics laws and forcefully sterilize minorities and the poor up until the 1970s?

Eugenics was often found in the political platforms of left-of-center political parties. A key proponent in Denmark, for example, was Karl Steincke, a father of the Danish welfare state, and several of the leading Norwegian eugenicists were also Social Democrats (N. Roll-Hansen, "Eugenics before World War II: The case of Norway," History and Philosophy of the Life Sciences 2 (2), 1980, pp. 269-98). Eugenics was adopted with enthusiasm by Tommy Douglas, later the pioneer of Canadian social democracy in Manitoba; by Fabian Socialists in the United Kingdom; and by the Progressives in the United States, all of whom favored social programs that, with the help of science, applied resources available to the state to building a more humane society.