The great defining problem of Western Marxism was the lack of a revolutionary subject or agent. Why is it that the working class does not complete the passage from in-itself to for-itself and constitute itself as a revolutionary agent? This problem was the main motivation for the turn to psychoanalysis, evoked precisely in order to explain the unconscious libidinal mechanisms which were preventing the rise of class consciousness, mechanisms inscribed into the very being (social situation) of the working class. In this way, the truth of Marxist socio-economic analysis could be saved, and there was no need to give ground to "revisionist" theories about the rise of the middle class.
For Zizek, Leninism (i.e. the creation of vanguard parties designed to seize power opportunistically rather than wait for the proletariat to rise on its own) is the appropriate response to the realization that communism is not as historically inevitable as Marx is said to have believed. Zizek's own eclectic mix of Marxism and Lacanian psychology is an attempt to diagnose the "fetishes" and "symptoms" through which people deny or deflect the reality of class oppression and the imperative of class conflict. I admire Zizek as a writer because I think his method has usefulness independent of his own agenda. His agenda, as I understand it, is the return of Leninism as a kind of fighting faith. This appeal to Lenin strikes me as a confession of a crucial failure of Marx. Marxism, I supposed, was a kind of appeal to reason, on the premise that proletarians would realize in time that their best interests would be served by taking over the means of production. Zizek is all too aware that this appeal has fallen on mostly deaf ears. He remains convinced that Marxism is philosophically and morally correct, in keeping with what he calls the "axiom of equality." Following Alain Badiou (albeit critically), he believes that Marxists should pursue communism by all means necessary because it is the right thing to do, regardless of whether they would win an opinion poll or an election, as a matter of "fidelity to the Event," the "Event" being the axiom of equality. He's enough of a realist to promise no perfection, perhaps not even any material benefit. But in his view the world must become communist because it must, because it is right, just as the project of "universal emancipation" must result in people becoming The People, those capable or worthy of living under communism. Marx's pretensions of science are replaced with moralism and literal appeals to faith/"fidelity." But Zizek has never given me a reason to exempt his own views from his own critical technique. I can imagine a conservative Lacanian (and perhaps I have to imagine one in the first place) diagnosing Zizek as one for whom Leninism is a way to avoid confronting the "Real" of "personal responsibility" or some other brute truth that would revel him to himself as a mere disgruntled loser. I don't say that that's the right diagnosis, but I don't know, perhaps from not reading him enough, whether Zizek has a way to prove it wrong if the analyst is as faithful to his own axioms of "freedom" or "personal responsibility" as Zizek is to his own. As far as I know, after all the brilliance, Zizek seems to be just another Leninist whose main argument for revolution is "because I say so."