"Certainly, the Russian state-capitalism, in which class relations are continued, cannot employ the Marxian science, for this science consists of nothing but the critique of those selfsame capitalistic conditions, which characterize Russia and every other capitalistic country. For the purpose of justifying the exploitation of the workers, the inequalities of income, and the accumulation of capital that exists there, the Marxian economic theories are certainly useless."
January 1, 1970
https://en.wikiquote.org/wiki/Paul_Mattick