You do know that Karl Marx wrote about capitalism, communism, atheism, and much more. What exactly do you mean by Marxism. I am always puzzled. It has been my experience that Americans think that socialism and communism mean a system whereby the government tells you what to do and removes all freedom.
In reality, there has never been a state with the kind of communism that Marx wrote about. Communism means there is no government — that everything is owned by the people. A business co-op is an example of Marxism. Plenty of them in the States. One of the most successful in the world is the one in Spain which employs some 90,000 people and has been going for nearly 80 years.
Yes, well, we definitely need a new economic system.