15 How is it possible that such a system, long since rejected scientifically and now proved erroneous by experience, how is it, We ask, that such a system could spread so rapidly in all parts of the world? The explanation lies in the fact that too few have been able to grasp the nature of Communism. The majority instead succumb to its deception, skillfully concealed by the most extravagant promises. By pretending to desire only the betterment of the condition of the working classes, by urging the removal of the very real abuses chargeable to the liberalistic economic order, and by demanding a more equitable distribution of this world's goods (objectives entirely and undoubtedly legitimate), the Communist takes advantage of the present world-wide economic crisis to draw into the sphere of his influence even those sections of the populace which on principle reject all forms of materialism and terrorism. And as every error contains its element of truth, the partial truths to which We have referred are astutely presented according to the needs of time and place, to conceal, when convenient, the repulsive crudity and inhumanity of Communistic principles and tactics. Thus the Communist ideal wins over many of the better minded members of the community. These in turn become the apostles of the movement among the younger intelligentsia who are still too immature to recognize the intrinsic errors of the system. The preachers of Communism are also proficient in exploiting racial antagonisms and political divisions and oppositions. They take advantage of the lack of orientation characteristic of modern agnostic science in order to burrow into the universities, where they bolster up the principles of their doctrine with pseudo-scientific arguments.
Source: Divini Redemptoris (Vatican.va)