In my opinion, because of the methodology used for the analysis of the economy. Marx identifies an economic phenomenon as it is presented, look into the different components an relationship between them and with other external elements, identify the laws that govern the different elements identified, and then try to explain in a scientific manner why the economic phenomenon is presented in this way and not in other forms.

He is not trying to find an economic theory to justify a political position regarding the capitalist economy,  but to explain the different economic phenomena associated with this economic system. He describe how the capitalism functioning and how the capitalists obtains their profits.

I agree that it is better to know both Mainstream (classical liberal economics that is taught everywhere today) and Marxist economics for better understanding of how the world functions. The trick is that they were almost never (apart from few universities in USA) taught together, perhaps due to ideological reasons.

But even the set of questions that they address differ. Marxist economics talks about structures without study of elements before. It addresses crisis of capitalism, struggle of classes, but not of some advantages of markets. Indeed, there exists a phase (like competition between many farmers or restaurants) that brings efficiency. Neoclassical economics also teaches what is optimal choice, while Marxist - not.

We know that several practices in former communist countries were negative: inability to supply sufficient amount and variety of food and goods, lack of incentives, etc. On the other hand, neoclassical economics has little focus on income and wealth distribution dynamics preferring to talk about a representative agent who is both worker and capitalist at the same time.

It's a joke?

What is a joke, Sergio? The question or the answers?

I would suggest that perhaps it is because Marxism offers a methodologically individualist, genetic-causal explanation. In other words, Marxism offers a time-based, causative theory based on individual, subjective human action, whereas Neoclassical economics often deals in aggregates and mathematical models that are divorced from causation and human action. (For example, under perfect competition, no market participant can affect the price. So where does the price come from? A mythical Walrasian auctioneer?)

But if this is Marxism's claim to significance, then I would note that there are several other traditions that offer a similarly methodologically individualist, subjectivist, genetic-causal explanation: in particular, the 19th-century French Liberal and the 20th/21st-century Austrian School. See, for example:

Hans-Hermann Hoppe, "Marxist and Austrian Class Analysis", in Yuri Maltsev (ed.), Requiem for Marx. Auburn University Press, 1993.

David Osterfeld, "Marxism, Method, and Mercantilism", in Requiem for Marx.

Ralph Raico, "Classical Liberal Roots of the Marxist Doctrine of Classes", in Requiem for Marx.

There are countless introductions to Austrian School economics, and I could almost pick one at random. But an excellent place to start is Alexander Shand, The Capitalist Alternative: An Introduction to Neo-Austrian Economics (New York University Press, 1984). 

And here is a nice encyclopedia entry about the Austrian School and its most notable ideas: http://www.econlib.org/library/Enc/AustrianSchoolofEconomics.html

I would suggest reading these essays I have listed, to see whether Marxism is valuable because of what it possesses uniquely of its own, or whether it is because Marxism shares several elements with fellow heterodox traditions (namely, the French Liberal and Austrian).

https://mises.org/sites/default/files/Requiem%20for%20Marx_2.pdf

Many radical economists believe that mainstream economics failure to grasp the true nature of capitalist society results from their unwillingness, or inability, to grasp the class-based nature of capitalist production. By beginning their analysis with exchange, mainstream economists fail to recognize the class based and exploitative nature of capitalist economies.

Calling this vulgar economics, Karl Marx believed that mainstream economists could never recognize the systemic and exploitative elements of capitalism. Once for all I may here state, that by classical political economy, I understand that economy, which, since the time of W. Petty, has investigated the real relations of production in bourgeois society, in contradistinction to vulgar economy, which deals with appearances only, ruminates without ceasing on the materials long since provided by scientific economy, and there seeks plausible explanations of the most obtrusive phenomena, for bourgeois daily use, but for the rest, confines itself to systematizing in a pedantic way, and proclaiming for everlasting truths, the trite ideas held by the self-complacent bourgeoisie with regard to their own world, to them the best of all possible worlds (Marx 1906, p. 93).

No. I do not think. The mainstream market is tightly controlled by Marxist economy and competition have no place in it. In general, Marxist economics tight state control prevents the emergence of the market and of course no capitalist economy with the opposite process, the result is the same. Islamic pattern-based economy where human values and divine word comes first humans can be evil goals

I agree with Michael Makovi

Objectively, Marxism has left a trail of poverty and failure in each of the countries where it has been applied.

Sergio-like peoples are very much right. I have to think that if I kill you with AK-47 firings and you are killed- Sergio's friend will say 'Sergio did not liked to live'! There are so many explanation like that.

Marxism can explain much better the market-economy because it point out the very basic development of it's faults, that is indigenous of capitalism and suggest its' recovery that had been developed in Communist societies like USSR. It has been killed by most opportunistic-civilized community like us (Gorbachev/s)- 'The Collusive Corruption' society.

First, we should understand 2 different things:

a) what Marx was writing (in fact, he was published and accepted, and his coauthor capitalist Engels was helping with money for joint research),

b) how the ideas of Marx have been implemented in different countries (former USSR, Eastern European countries in 1950-1990, China, Cuba, etc).

If we are talking from academic perspective, the works of Marx are complementary to mainstream economic and social theory; they address some new issues (like emergence of classes and their struggle), but they do not elaborate many things that classical economics does. In fact, it is possible to find link (but nobody wants to do it). These examples are from classical, non-Marxist economics: a) game theory studies sharing of surplus, b) monopoly can abuse consumer (and also worker, if it is the only employer). In an extreme case of cartel agreement between all capitalists regarding low wages, the surplus is created and exploitation takes place. But emergence of classes is technically impossible in classical economic theory, where all individuals are atomic and have self-regarding preferences.

As for implementation, none of the countries had perfect implementation of the ideas of Marx. Russia was the first and did wild mistakes in the first years, when "red terror" has killed not only capitalists but also many peasants, priests and other groups who have never exploited workers. The example of post-communist countries of Eastern Europe shows that they do not want to return to their Marxism. On the other hand, China still keeps partly Marxist ideology although it has reformed it substantially. Maybe China is doing transition better than former USSR countries, who jumped from this ideology to wild market, while China had slow evolution and reached big success in economic growth in the last 25 years.

Dear Yuri, you are academically try to defend your logic that should be. Yes it is very short place to continue such a grave subject with few words. Economical amplification of Marxian theory in market economy never be coincided with political venture of any countries whether it is USSR or USA like things. Just for 'killing' reason of one country, USA is always toppest, that never will overcome as long the 'Godfather'-ship of capitalism will continue. 

Marxism was only a theorem before 1917 and it first time happened in vivo. If we consider the famine or malnutrition scenario of this planet then we have to consider the best one to choose for basic human right to live with one’s basic requirements. We, who are participating in such discussion, have to think that how much time you are wasting just for argument sake and enjoying it. But a farmer of agrarian field has little choice for wasting time and if he/she does then harvest will lost. We will buy the very food from others farmers’ production and the ‘first’ farmer will die without food which he/she failed to yield.

After so called initiation of civilization, capitalism is continuing with just little break of the very negligible socialistic developments that are really iconic to its’ dead-critic also,

What is the alternative to us to implement measures to save all dying peoples worldwide? Capitalism is a total failure but killings of  millions who wanted peace and food only.

Taken in contrast with "capitalist" dogma, Marxian economics supplies the necessary parts of the equation, explaining why the world is perhaps moving towards a socialistic economic system as predicted by Joseph Schumpeter in his 1942 book:Capitalism, Socialism and Democracy. The point is that every system sows seeds of its own demise at a certain point. That was the case with Marxian economies. The question is whether the epoch of capitalism is over, and with its demise a new epoch of social-democratic system is up the horizons.

Dear Lew

I agree with you. But, would not you look at the fact social-democratic and liberal democratic system are phases of capitalist expansion strenghthening more the roots of capiatlism.

Thanks.

Israr

Dear Mohammad Israr Khan,

Very interesting point, and here is where perhaps Marx departs from Schumpeter. A Marxist may admit the idea that a movement towards socialism may lead to a hybrid system that has capitalist elements in it. Even allowing the co-existence of both. Thanks in part to dialectical materialism. A case-in-point would be the current "one country, two system" adopted by China. Where elements of capitalistic, free markets are coupled with communist (socialist?), Marxist ideas. However Schumpeter seems to subscribe to transformative change, where destruction creates. Thanks in part to "creative destruction". The "destruction" of capitalism, or its demise paves the way for the creation or the ascendancy of a new epoch rooted in socialism. In this respect, it would be a largely socialist system with perhaps legacy features from capitalism. It will neither be capitalism in a new guise or a complete reversion to capitalism as we know it. This is the trend one observes in Europe, the US and parts of Asia where the role of governments and the state in market dynamics is getting larger rather than smaller. So whether it be former communist or capitalistic economy there is a predilection towards socialism as the state of economic affairs would demonstrate at this point. 

Following are some critical questions on Marxian Economics:

https://islamiceconomicsproject.wordpress.com/2013/12/02/critical-questions-on-marxian-economics/