Over at Skepticlawyer, I was challenged on my claim that
Leninism (or derivatives thereof) proved to be the only effective way to politically operationalise Marxism
The claim was a little over-stated; Leninism (or derivatives thereof) proved to be the only distinctive effective way to operationalise Marxism. Marxism did motivate the formation of trade unions and Social Democratic political parties (or, at least, providing the animating ideology).
But, of course, there was nothing particularly distinctive about that in that proved to be entirely possible to have trade union movements and working class-based political parties without any significant Marxist element at all. And, to the extent that there was a distinctively Marxian element, the effect also proved to be reactionary.
For the more identified with Marxist ideology the Socialist/Social Democratic Party was, the larger the Leninist offshoot after 1917. The larger the Leninist offshoot, the larger the countervailing Fascist/Nazi/Authoritarian movement was.
Moreover, the larger and more threatening the Leninist offshoot was, and the more identified with Marxist ideology the Socialist/Social Democratic Party was, the more ignored rural voters, particularly peasant smallholders, were and the more the Fascist/Nazi/Authoritarian Right movement was able to mobilise them as a voter and support base.
Moreover, Leninism provided Fascism and Nazism with a model of how to operationalise politics. This is most obvious with Mussolini--as he both wrote about it and came directly out of the same radical-Left socialist milieu as Lenin et al--but not much less so with Hitler. If Lenin was Marx + Robespierre -- as Lenin Jacobinised Marxism -- then Mussolini was Mazzini (or perhaps Garibaldi) + Robespierre while Hitler was Gobineau + Robespierre (with added anti-Semitism). And Lenin provided the model of how to operationalise total politics for whatever one's project was (national greatness in Mussolini's case, Aryan race-purity-and-dominance in Hitler's case).
Those Socialist/Social Democratic Parties that remained on the free side of the Iron Curtain effectively dropped the deadweight of Marxism, going on to prove how unnecessary Marxism was to have an effective Labour/Social Democratic/Socialist party and trade union movement. Even beneficial, since an official Marxist ideology got in the way of coalition-building, scared (some) voters while jettisoning it permitted a more effective electoral and policy pragmatism without the ideological blinkers.
The later Eurocommunist movement was attempt to distance the Parties involved from the the deadweight of revolutionary Marxism (i.e. Leninism), becoming more like the Parties that had Never Gone There or had effectively dropped Marxism. With precious little actual Marxism after that was done -- and the more there was, the less successful the Party tended to be in the longer term.
A for the involvement of Marxism in various progressive social movements, the history of the Emancipation Sequence in the Anglosphere (abolition of the slave trade, then slavery; Catholic Emancipation, Jewish Emancipation, Female Emancipation, the civil rights movement, indigenous emancipation, now queer emancipation) also demonstrates how unnecessary Marxism is and was for the sequence.
Certainly, Marxists got involved in the later movements, but that was a very mixed blessing. They tended to get in the way of the broader coalition building that allows such movements to succeed by making the movement seem more broadly dangerous, provided broader ideological baggage that diverted energies and focus that generally got in the way.
On balance, Marxism has been far more a destructive deadweight for progressive movements than a benefit. Not least for its tendency to give its adherent the belief that they know what people should want/need rather than what they actually want/need.
It may not be a coincidence that the only surviving full Marxist regime is the most atavistic of the lot -- the quasi-religious dynastic theocracy of North Korea. By so thoroughly embracing the atavistic core of Marxism -- this notion of prophetic understanding of the direction of history far greater than other mortals not blessed with understanding of the true doctrines which will provide a salvation that will eliminate all alienation -- the Kim Family Regime has continued when elsewhere Marxism as an significant political force has collapsed, yet another casualty of the historical tsunami of modernity.