Science does not depend on who believes what. Your whole argument is silly 'reasoning'. It does not matter whether Marx believed in evolution or creationism, in an OT god or a NT god, or a Hindu god, or no god. The business of science is sorting out what are valid explanations of natural phenomena, and this is independent of specific individuals. If Darwin had not developed the idea of evolution, someone else surely would have, since the observable world points to it.
As far as what Hitler, Marx or Stalin may have thought--if they thought--it makes no iota of difference. This is a kind of argument from authority in reverse. Science does not depend on authority figures to be valid. Nor is it smeared by bad people who accept it.
For example, it is likely that Hitler and Stalin believed in motherhood and gravity, too--would you then say that motherhood and gravity are, therefore, suspect and invalid?