117 But what if Socialism has really been so tempered and modified as to the class struggle and private ownership that there is in it no longer anything to be censured on these points? Has it thereby renounced its contradictory nature to the Christian religion? This is the question that holds many minds in suspense. And numerous are the Catholics who, although they clearly understand that Christian principles can never be abandoned or diminished seem to turn their eyes to the Holy See and earnestly beseech Us to decide whether this form of Socialism has so far recovered from false doctrines that it can be accepted without the sacrifice of any Christian principle and in a certain sense be baptized. That We, in keeping with Our fatherly solicitude, may answer their petitions, We make this pronouncement: Whether considered as a doctrine, or an historical fact, or a movement, Socialism, if it remains truly Socialism, even after it has yielded to truth and justice on the points which we have mentioned, cannot be reconciled with the teachings of the Catholic Church because its concept of society itself is utterly foreign to Christian truth.
Source: Quadragesimo Anno (Vatican.va)