The "social justice" folks better remember that even if some few passages of the Bible may be favorable to communism, the general spirit of its doctrines is, nevertheless, totally opposed to it:
Privately entrusting resources to St. Peter, in subservience to God, differs greatly from “robbing selected Peter to pay for collective Paul” through a distant bureaucratic apparatus inspired by the humanist god of power. The Bible never endorses involuntary socialism administered by secular governments.One of the most recent examples of the above is Brazil, where it quickly went from social justice to social engineering; where the very same religious organizations that originally supported the government's anti-poverty efforts are now being marginalized. Where the choice for many is now - conform or leave the country. Not for nothing did Bishop Fulton J. Sheen say that if the "social justice" crowd bothered to look for a patron saint - that would be Judas Iscariot.
Communism fails except as augmented by fear (and ultimately there too), because forging “New Socialist Man” remains forever beyond the state’s grasp. Only God can change men’s hearts. Our base instincts betray us. When we see someone slacking and still taking – we produce less. When we see others taking beyond their share – we take more too. Without private property and opportunities for profit through honest toil, living standards stagnate.
Any movement must deal with realities and thus superficial similarities with other systems will materialize, but properly understood, Marxism is the absolute denial of Christianity – precisely as Marx intended. Where Marxists seize power, Christians are always persecuted and atheism is enforced, usually at a steep cost.
Update: Pope to Social Justice Groups: Activity must be Competent and Transparent.