Slavery, Supply, Demand

One of Marx's sharpest insights only touches upon a problem for any Political or Economic system.  According to his analysis, it follows from the principle of Self-Interest that the Capitalist seeks to pay a laborer only enough to ensure a return  to work the next day, which they will do if the labor supply far exceeds its demand.  Thus, since the 'freedom' of a laborer to refuse such work is nominal, the condition is equivalent to Slavery.  However, Marx seems to stop short of a further of examination of that relation, which predates any Political or Economic theory.  Likewise, what Plato misses in his account of social 'necessity', is the need for drudgery tasks, including, notably waste disposal, e. g. mopping, sweeping, etc.  Now, in itself, the demand for such labor is perhaps both high and perpetual, but, the supply, i. e. those willing to perform it, is minimal, at best.  Hence, enter Slavery to generate that supply.  But, since those tasks usually require little special skill, even Marx's formulation of 'to each according to his ability', does not define who in a division of labor subsequent to the socializing of the means of production is to clean the toilets in a factory at the end of the day.  Even the speculation that one day, robots will perform such drudgery, does not address who cleans the toilets in the factory that builds them.  So, rather than a peripheral problem in Political or Economic theory, the conditions to which Slavery, in its various guises, has been the traditional solution, is an essential one.