Now, my understanding is that Marxism is a kind of analysis of capitalism. Marxism is a theoretical framework. Marxism is a diagnosis not a prescription. Karl Marx, himself, did not write or concern himself with communism or socialism or any other -ism as "The Answer," I understand.
Marx saw his role to be that of an analyst, giving the best analysis he could of a system he thought had outlived its usefulness; and he wanted to provide the intellectual tools that activists would need to overthrow capitalism. But he didn't say what should be erected in its place.
Marxism allows for various kinds of interpretation of capitalism along broad lines of agreement. Most Marxists, as far as I know, advocate for an alternative to the way work is structured, so that the workers producing the "surplus" get to be the same ones that decide how it is distributed. In Latin America many socialists have become presdent and obviously think the solution lies in some kind of state planning of the economy as the answer....
What your question gets at, magodis, is the "law of the jungle" nature that capitalism, in my opinion, exhibits, particularly in this so-called "neoliberal" phase. Most Marxists are either socialists or communists, its true; and I suppose they would therefore rather see socialism or communism become the order of the day.
I suppose what it comes down to, quickly, is that Marxists agree that there has to be some kind of more rational social control of what's called the "surplus product," the profits. Actually, some Marxists and Anarchists think that we need to move to a zero-growth economy, one in which there are not going to be any profits for anyone gamble away.
We should be able to have a dynamic, technologically innovative economy without expanding GDP or GNP, which, hopefully, would mean a drastic cutback in the human contribution to global warming and a great easing up on the use of natural resources (hopefully petroleum products will be banned sometime soon).. There are many different things one might prescribe as the antidote to our various social ills; just remember Marxism itself is merely a theoretical framework, a style of analysis.
If one idea unites Marxists, I would say, is that you cannot have infinite growth on a finite planet with finite resources.