One of the preeminent aspects of Marxism is the conflict between the capitalist, who owns the means of production, and the producer, who is represented by the working class that executes the labor required to bring the commodity-value to the table. It is precisely this conflict of interests, the competition for the value this operation provides, that leads to working-class upheavals across the globe.
Marx noted the upheavals in his day, and suspected that a new class would soon rule over the means of production once these conflicts were resolved. In terms of the shifting of value to the hands of the working class, this indeed occurred across the globe during the innovation and industrialization of many of the high-infrastructure societies of today - a feat that the expanded employment of labor helped accomplish. This expansion of employment has helped (or is helping) create an high rate of value-exchange: when high-consumption wages (lower class wages go primarily to consumption) are a large percent of income and total value('currency'), a greater sum of money returns to the consumer to augment aggregate demand.
What this amounts to is a buy-off of the working class. But this is not the only method of population-control employed by the preeminent owners of the means of production. Much of mainstream media, and indeed the culture as it has been defined by institutions for centuries, supports a one-sided narrative of economic processes. The free-marketeers propose extremist reversion in the benefit of the largest stockholders in private property. The "neo-keynesians" propose mild measures to sustain an inherently exploitative, self-devouring system.
The third option, socialism, instead proposes the re-distribution of the stock of the means of production. Rejecting the quixotic regard for extant private property (for many of the same reasons regarding government graft that libertarians often regard exchanges as 'illegitimate'), socialists propose that the very actors which give the material life to the means of production - engineers, miners, janitors and consumers to name a few - ought to be in management of their own labor as it courses through the means of production.
Insofar as the moral legitimacy of such a program is concerned - I don't think there can be any contest. The value of a social structure is directly proportional to the value it offers the members of society. For this reason, capitalism has been one of the best structural relations that humans have had for a long time. But its fatal flaws drive it to precisely the same autocratic processes of incentivization and mechanization that the old kingdoms are built on: ownership or leverage over key aspects of the social economy. The moral basis for the social seizing of the means of production are tied up in the existence of an institution as a socially-relevant structure.
Marx saw one of the most turbulent times in the history of capitalism. Indeed, it appeared that the richest capitalist states were doomed to the ultimate whims of an angry mass of exploited peoples. He certainly felt that successful class war was far more imminent than it proved to be. But precisely the same conflicts which Marx assessed have come about in nations all over the world - China's industrialization is seeing increasing unrest, a problem mirrored in the industrialization and peasant-dispossession in India and Pakistan.
What Marx was keep about was the expansion of the capitalist market. What he may have under-appreciated was just how expansive the market can be: increasingly, new needs are being fulfilled and new capitalists are seizing key resources to meet those needs. The dynamics of the market are reaching limits that threaten the viability of cross-class collaboration to the average worker.
I am very uncertain of what the consequences of today's political economy will be. It is clear, though, that capitalism - or any system built on the leverage, held by few, over the means of production, is inherently unstable. The demand for ever-expansive profits can only be maintained by increasing value returned to the working class - a structure which obliterates investor faith in its expected returns. What is further clear is that the pauperization of the first world is not slowing, and it will not be accepted once the working class has lost all it has to show for the system.