We can define a fact as an observation backed up by such a preponderance of evidence that no useful purpose would be served by doubting it. - Mordechai Ben-Ari

Social Darwinism and eugenics are unscientific in two aspects. First, they commit the naturalistic fallacy, which is the assumption that what is, must be. The fact that the natural environment selects for reproductive advantage does not mean that we, as humans, should be forcibly selecting people according to some preconceived notions. The second nonscientific aspect of these movements was their narrow interpretation of the meaning of fitness. In evolution, this simply means fitness to survive and reproduce, not fitness according to some externally imposed criteria.
Darwin himself never engaged in these speculations, nor did he support these perversions of his theory.

The scientific point of view is that such claims of postmodernism are a travesty that comes from mixing ideology and politics with science.

To brand evolution as “just a theory” is the finest compliment one can confer on it!