Karl Marx, it is said, objected to Christianity not because it was untrue but because it did not live out its own truth. Christian socialism was an effort to apply the teachings of Jesus to a society without the intervention of the church, or of Christian theology, and it was in this sense that the Roman Catholic church regarded communism as a heresy; a partial and incomplete version of Christian truth. Communism was guilty of a number of heresies and errors, not the least of which were its idolatry of the state, its denial of individual human dignity, and its totalitarianism, but what made communism--and socialism, its less pathological relation--was the similarity rather than the dissimilarity that it bore to the Christian gospel and the fundamental teachings of Jesus.
-Peter J. Gomes, The Scandalous Gospel of Jesus, p 70