Your quite right, this article is written with a very detectable tone of bad faith. The chief evidence I see given in the text for Marx being a genocidaire is spurious and a misrepresentation. It’s lifted from a text published in the New York Tribune called “Forced Immigration”. In the passage, Marx expresses doubts with Ricardo’s theories of surplus value, in fact he was making a point about “compulsory migration” and contrasting it against its modern variant. Frankly it has nothing to do with race extermination or ethnocide, one quite literally has to make that up into the text. Stalinism and Nazism have long been considered discrepant forms of fascism or at any rate totalitarianism. Both are political proscriptions for absolute state control over the private individual and the practical negation of the concept of the citizen. They rely on application of historical revisionism to fit either ethnic or ideological claims, or when the internal contradictions weigh to heavily, they export their violence on others to relieve the pressure. Marxism is a theory of history, or rather if you like, it’s a method of historical analysis from the standpoint of the material (materialist conception of history). Anyone who tells you it’s a purely economic or exclusively political theory hasn’t read a page of Marx, nor if they tell you that one of its central organising principles was ethnic cleansing.

But as you seem to suggest, one doesn’t need to be a Marxist in order to be a Socialist, nor a Socialist in order to be a Marxist. That a number of self identified socialists like Che harboured unacceptable views on Africans or indigenous people does not mean the entire ideology is axiomatically defined by it. Marx did express some quixotic views on British occupied India in the Tribune and they are rather condescending at times. But he firmly came down in then end on the anti-colonial side in an 1853 column on the subject calling it a “profound hypocrisy and inherent barbarism of bourgeois civilisation”.