One of the biggest reasons why communism has not happened, is, as the other responder said, Marx had not heard about the welfare state, and other modern regulations to capitalism, like unions and socialized health care.

It is easy to look at Russia as a failure, but bear in mind that in 1914 they were unable to even defeat Austria in combat, and by the 1960s were undisputably the second most powerful nation in the world. While I do not even begin to justify the human rights abuses that occured under the Stalinist regime there are other causes of the failure of the Soviet Union than simply that their economic model was flawed.

There is considerable evidence that throughout the Cold War the Russians wished to disarm but NATO would not allow it. Western Europe and America essentially spent the Russians to their death, forcing them to spend higher and higher precentages of their GDP on military and not economic or social spending.

Furthermore, it is my contention that if communism is possible (and to a limited degree it has great success in Canada and Northern Europe) than it is important for it to occur in an open democracy. No society can be expected to survive the withering constraints of a dictorship, be it of one man or the proletariat.

Is communism possible or just a pipe dream? Look at the Kibitizs of Isreal, the Mennonite farming communities of rural Ontario, thousands of African tribes, the Native Americans of yesteryear and the conquering Mongols. You tell me.