I had an argument with my Calvanist grandparents today on what is the difference between Catholic social justice and Communism since they seemed to think that anything against capitalism "must be Communism." Well I know I'm probably preaching to the choir here but I will go into some differences between the Catholic system of social justice and the Marxian system.
1. Catholic social justice acknowledges the right to private property. The key tenet of Marxism was that property is given out collectively by the State. Social justice teaches that everyone has a right to private property to call their own, however the rich also have the duty to help out those less fortunate than them as well.
2. Under social justice the worker is a human being who is supposed to be given help and prayer to help his current condition. Both capitalism and Marxism sees workers as simple means of production. Capitalism sees workers as simple ways to make the rich capitalist grow rich at the misery of others, while Marxism sees workers as means of production, which can be liberated and revolutionized into the "dictatorship of the proletariat."
3. Marxism sees perpetual class warfare and conflict that will not be resolved until the bourgeoise is destroyed and the "dictatorship of the proletariat" is put in its place. Catholic social justice sees class harmony and peace WHEN the necessary social conditions are put in place that can help alleviate the sufferings of the worker. The worker has the duty to agree to the work that the industrialist has given him, while the rich factory owner has the duty to help his fellow workers out and respect their religious observations. Capitalism breeds class conflict as well since the worker is not a human being, but a simple robot or "cog in the machine" among other faceless entities who work their life away.
4. Under social justice a "living wage" is provided so that the man can support his family. Both Marxism and capitalism are extremely anti-family, capitalism because it supports women in the labor force, as does Marxism, along with the Marxist and liberal doctrine of feminism.
I could keep going on but that is some of the main points.