Plato's views on the division of labor constrast sharply with those of Marx and Engels. Both parties speak of changes from what was, at their times, the status quo. Plato's Republic sketches an ideal society, including an economic structure. Karl Marx and Friedrich Engels propose communism as the inevitable future. The economic system of the Republic is based on the division of labor. The communistic German Ideology states that the division of labor is a prerequisite of capitalism, and that both should be removed to make "personal freedom possible" (pg. 83). Plato is writing about an ideal, the communists about what they see as the fate of humanity (in an admittedly materialistic and therefore non-idealistic way), and the two views are contradictory. I refer to Marx and Engles throughout as "communists", but it is quite possible that they did not see themselves as "communists".
The Republic is the result of interdependency: "a state comes into existence because no individual is self-sufficing" (pg. 55, Cornford). Plato's state and economic systems are based on a contractual, give and take, basis. One puts something in, and one gets something out. What one puts in is determined by his abilities. Plato makes categories into which each person shall fit. Division increases as the state nears the ideal, so that one man is a cobbler and a cobbler only, or a smith and a smith only. Things are done better "when every man is set free from all other occupations to do, at the right time, the one thing for which he is naturally fitted" (pg. 57). The division of labor follows from idealism: the best gardener reflects only the ideals of gardening.
Marx and Engels synonymize [equate] "division of labor" with "the fact that intellectual and material activity - enjoyment and labor, production and consumption - devolve on different individuals ..." (pg. 52). The division of labor means exploitation; it means some work and get nothing, and other get and work not. They see capitalism as the contractual economic society gone awry. The inevitable balancing of this lop-sidedness occurs with the abolition of divided labor, the abolition of classes.
Platonism and communism are mutually exclusive on at least two levels: idealism vs. realism, and whether or not to divide labor. Divided labor in the Republic produces a harmony of the whole, while in the German Ideology it produces "alienation" because an individual is "imposed on" to seek other than his "particular interest" (pg. 54).
The reasons for these opposing views are the purposes of the books. Plato is seeking to define justice. He does this through the development of an ideal state, which has class divisions. Justice he sees as the constructive co-existence of the parts which make up the whole, be it the members of a civilization or the parts of a human.
Marx and Engels wish to present communism as the inevitable resolution to the ills of a capitalistic society. Marx and Engles are dealing with things which they feel can or will come to pass, not platonic ideals. The difference between motives for writing produced different products - not that, given the same motive, they would be similar.
Plato's value is in the good, a somewhat passive knowledge of the good and the ideal. His purpose was to enlighten on such subjects as justice. The communists wish to be part of evolution, wish to bring change. For them, the abstract is pointless, a hinderence, and a waste of energy better used for revolution. The German Ideology and the Republic are different by authorship, by purpose, and by their natures. Their disagreement on the division of labor cannot be resolved.