From the article, if you took the time to read it.

This determination to have the complete, closed story, or model, the final word, is something I cannot forgive Marx for. It proved, after all, responsible for a great deal of error and, more significantly, authoritarianism. Errors and authoritarianism that are largely responsible for the left’s current impotence as a force of good and as a check on the abuses of reason and liberty that the neoliberal crew are overseeing today.