Who agrees that Marx, himself, was anti-bureaucratic, yet, dictators, who claimed to be Marxist, used bureaucracy anyway for supposed Marxism? How? Why?
I assume the kind of dictators you have in mind are those running regimes such as the USSR and its client states. They were Marxist-Leninists for whom Marxism was an analysis of capitalism and Leninism concerned the organization of "socialism". But Lenin's template for "socalism" was German state-capitalism - he said so himself. Neither Lenin nor his successors were ever out to build "Marxism"; they were busy building state-capitalist regimes dedicated to the generation of surpluses, their investment and the subordination of life to work - just like their Western counterparts. Only the mix of planning, markets and police state methods varied. Confusing Marxism with Soviet-style state capitalism & its police state was a Cold War ideological myth perpetrated by Western capitalists and their spokespersons to facilitate the repression of Marxist critics of capitalism in the West. The USSR had its own myths about Western-style capitalism for parallel purposes.