Marx's diagnosis of what is wrong with modern industrial society is developed by analysis of power ratios of labor and capital. The basic argument is that capital, which controls the means of industrial production, including but not limited to labor is always in control. Labor is at the mercy of capital control because more laborers are always available to serve the needs of capital, even if some laborers withdraw their work value from the industrial marketplace.
Marx uses the terms alienation and division of labor to describe what is wrong with modern industrial society. The proletariat, or labor, is in a position of irony. Workers know that without private property there is no production to be the means of. And if that is the case, then the proletariat has no role, function, or place in society, i.e., no claim to life itself. But at the same time, workers function as servants of capital to meet basic survival needs. Thus labor sinks further into oppression, toward slavery.
Because the structure of society is the agent of social ills, only destruction of society defined by capital and labor classes will suffice. Liberal reform does not go far enough:
You are horrified at our intending to do away with private property. But in your existing society, private property is already done away with for nine-tenths of the population; its existence for the few [i.e., capital concentration and accumulation] is solely due to its nonexistence in the hands of those nine-tenths (Marx, "Manifesto" 486).
Class power, held by bourgeois capitalists, links to political power, which links to industrial-economic power over the laboring classes. When one kind of oppressive power is abolished, so will the other kind be. Power ratios will be transformed.
When . . . class distinctions have disappeared, and all production has been concentrated in the hands of a vast association of the whole nation, the public power will lose its political [= oppre...