One of the things that often confuses people is that communism just doesn't seem to work in practice.  When Karl Marx first wrote Das Kapital, it seemed like a very simple and basic idea.  "From each according to his ability. To each according to his needs."  The promise would be that everyone would work for the good of all, and no one would be left behind to be a beggar on the street. 

In a world dominated by an entrenched political ruling class, and a large population of unskilled serfs, this was definitely a revolutionary idea.

But Karl Marx was not a business man.  Nor was he expereienced or knowledgable when it came to the movement of goods and services.  His treatise was written based on the masses who were toiling in the new factories, assembling products for low wages while the owners and merchants were reaping all the rewards.  He belived that only the workers were adding value to the product, and therefore the workers should be receiving the rewards.

On paper this sounds just about right
In theory this would be a utopia where eveyrone works equally and shares the rewards equally
In practice it will never work in a modern world.

What Karl Marx never understood was the origins of capital and the divisions of labour that were going to exist in the future.

These are important issues.  Capital is the driving force behind any business, and labor skills are what employees are providing to a company.  Because Karl Marx never understood these two factors, he assumed a much simplier situation wherein the masses could start and run corporations without some of the specialized skils we now recognize as necessary.  Although the liberals refuse to accept this reality.

First, no business can start without some level of investment, and the more complex products usually require much higher investments.  When you look at a factory, and don't wonder where all of the equipment came from, its easy to think, "the workers should be in charge and own all the product that comes out."   However, for that factory to be built a large amount of money had to be gathered and then invested into setting up the facilities.  This money is only giong to become available if those that currently possess the money believe that they will receive dividends and interest in exchange for the use of their money to start the business.  The masses usually do not have the money to hand, and to take a factory over after its construction amounts to theft.  So communism will always begin through the taking from those that invested their wealth in order to establish its reign.

And then you have the problem of labor itself.  When Das Kapital was written, the industrial world we know of today didn't exist and to most people wasn't thought of as possible.  For the masses there were only a few opportunities.  You could stay on the farm, you could join a military unit, you could attempt to get an apprenticeship with a craftsman, or you could work long hours in one of the new factories, where almost all work was unskilled.  Having an education was rare and the specialized skills to make and repair equipment were highly valued.  This was not something the writer of Das Kapital worried about, and he missed a crucial economic factor.

People who have taken the time to learn specialized skills do so because they expect higher rewards.  Doctors, and Lawyers don't just appear out of nowhere.  These are men and women who have spent years of their life learning skills that they believe will be valued.  In exchange they hope to receive a high salary during their working years.  But if you try to make a society where all receive rewards "equal to their needs."  you take away the incentive to learn the specialized skills.  And our modern society has thousands of unique specialties that must be practiced in order to keep the economy running.  Any true communist society quickly discovers that the vast majority of its people refuse to expend extra effort learning and practicing special skills for no additional reward and the economy tends to suffer greatly.

Its all a false promise of communism.  Karl Marx saw that factories were nasty places to work, with a high casuality rate and very low pay for unskilled workers.  He attempted to create in theory a world where these proles would not be exploited by the merchants and industrialists of the day, and ended up writing a book that has had far reaching and terrible consequences.  Today the arguement always is "True communism hasn't been tried.", but that is merely an inadequate excuse for the failures of a theory that had left out vital facts when developed.  Until those flaws are acknowledged, any attempt to create a communist "paradise" will only result in more deaths from famine and civil unrest in those regions that attempt to ignore humanity itself, in their quest for Erehwon.