It assumes that reality includes an objective and knowable "good," that human being is potentially a fully "rational" being able to know and actualize this "good" in a good life, and that realization of this potential requires passage through a set of developmental stages in each of which a characteristic degree of historically diminishing irrationality (in the sense of Hegel's idea of the "passions") dominates. The realization of the potential in a "true realm of freedom" is associated with a "feeling" - "eudamonia" - to which any rational being would say "stay."
These assumptions are inconsistent with "moralistic" judgments; the only sources of action inconsistent with universally valid ethical principles are ignorance and impracticability.
They are consistent though with "ethical" judgments, i.e. with judgments of the consistency of feeling, thinking, willing and acting with these principles.
The capitalist/wage-labour relation is "unethical" in this sense; it's inconsistent with the ideal ethical relation Marx (and the ethical tradition to which his ideas belong) elaborates as "relations of mutual recognition." For instance, in it wage-labourers are "exploited." They are treated as "means" rather than as "ends," as "human resources." This is inconsistent with an ideal relation of mutual recognition.
Ted