But the core of Marx ideas are an analysis of value, labor, production and surplus. They have been very useful for analysing the global recessions and over-production crisis, the concentration of wealth and lowered wages that we see today vis-a-vis the 70s.
They're not some loonie ideas about the size of skulls or a master race.
They are, however, deeply flawed. The labor theory of value is the core Marxist economic principle, and it is incorrect. Marx also doesn’t deal with the knowledge problem, and he doesn’t adequately address the value of laborless resource. If we move on from there, his summation of the trend of history is also incorrect. Societies have not tended toward Communism but instead toward Fascism (corporate and governmental merger coupled with totalitarianism) at the level of countries, and toward a neo-feudal order globally.
Of course Marx is wrong, he's a scientist. The work is never "done". And everyone is ofcourse free to critique the theories - but I find it rather extreme to view his theories as deranged garbage on the level of eugenics or social darwinism.
This is absurd. Nobody would ever say “But the core of Nazi ideas are an analysis of genetics” as though that excused anything. The fruits of both ideologies were hellish disasters, and the oppressed/oppressor dichotomy of Marxist thought is every bit as poisonous as the aryan/non-aryan dichotomy of Nazism.
Marxism can easily be adapted to support any group's resentful revenge fantasies so it's seen with much better eyes than a German man's resentful revenge fantasies.
They're not some loonie ideas about the size of skulls or a master race.