While we may very well be defining “socialism” differently, I think it’s worth commenting on what the Catechism actually means in this context.
“The Church has rejected the totalitarian and atheistic ideologies associated in modem times with ‘communism’ or ‘socialism’.”
Here, it is quite clear that what is being rejected is not limited to certain principles of socialism, but complete ideologies based on socialism or communism. If entire ideologies based on these two are condemned, then we can logically conclude that socialism and communism, as ideologies in their own right, are to be rejected as well. Again, I am not speaking of certain aspects of socialism, but of socialism as a whole, taken as an entirety. It’s not only certain parts of socialism that are incompatible with the Faith. Its fundamental principle, as well as the end to which it is directed, makes it is contrary to Catholic teaching.
In rejecting the ideologies of socialism and communism (which will inevitably lead to full-blown atheism), the CCC simply repeats, though in a more vague/general sense, what the ordinary magisterium already taught:
“You are aware indeed, that the goal of this most iniquitous plot is to drive people to overthrow the entire order of human affairs and to draw them over to the wicked theories of this Socialism and Communism, by confusing them with perverted teachings”. —Pius IX, Nostis et Nobiscum
Socialism has been rejected not only due to some of its principles, but because its fundamental concept of human society is contrary to the Faith:
“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”. —Pius XI, Quadragesimo Anno