When did communism become associated with Athiests and Evil? Was it when Stalin murdered more people than Hitler?
Or was it from all the heresies that come out of false religion?
Communism as it is known today was invented by Karl Marx. Prior to that time there were ideas present in some societies that leaned towards communism, or borrowed some elements of communism. However, for the most part, communism is a purely modern idea.
Given this, communism has been, from its inception atheistic and evil. Karl Marx, from the very beginning, built atheism into his social theory as a key component.
He recognized that organized religion, especially Christianity was completely antithetical to his ideas and would always be a natural enemy of the society that he envisioned.
In most societies it is always the lower classes and the common folk who are the most religious, the most conservative, and the most pius.
Marx's views required these people to rise up and over throw the 'higher' classes. Marx's view was inherently revolutionary, and required the common people, the working class to be revolutionary.
This creates a kind of irony since the common people are usually the most conservative. The real revolutionaries, and through history those who have actually lead communist movements have almost always been educated elites, not the common working man.
The common working man always becomes a mere tool for the social revolutionary theorist to play with in trying to gain power and test his theories on society.
Anyway, Marx recognized religion as his cheif enemy in turning the common workers into a revolutionary force. He expressed this in the now famous phrase that religion is 'the opiat of the masses'. IE religion is a drug that lulls them into inaction.
Thus Atheism is a foundational part of communism and has been since it was formulated as a social theory.
Now, addressing JimR and the quote from the Catholic encyclopedia
The quotes you posted really don't help your case, at least that I can see.
They confirm that communism is defined by lack of private property and that mere corporate ownership of capital assets (allowing other assets to be privately owned) DOES NOT qualify as communism.
Also, the statement that religious orders exhibit "some of the features of communism" doesn't equal "they are communist".
To say "it has some communist features" logically requires that the thing itself is not communist. Otherwise it would be a redundant statement. such as communism has some communist features". That kind of statement doesn't make sense.
The statement only makes sense if the thing in question (religious orders) are not communist but do have some features which are included in communism, or which resemble elements of communism.
In terms of social systems, there are three defining points of communist social theory.
#1 lack of private property
#2 the community is totalitarian
#3 membership in the community is not voluntary
Also, you differentiate between Marxism and communism. I agree that there certainly have been communal elements of many societies through out history. However communism as a social theory pretty much originates with Marx.
The ancient roots of communist theory are often held to be found in Plato's Republic. There is some basis for this, however, what Plato described is not a true communist society. In fact it consisted of three distinct classes and could be described as more of a caste society than a communist society.
It is sometimes held to be communist because the community described was what moderns would call totalitarian and essentially the individual people existed only for the good of the community.
(it should also be noted that in the context of the book it is not at all clear that Plato is actually endorsing this view.. it is in my opinion a satirical view).
Other than that, there is nothing more that even smacks of real communist theory until you run into the enlightenment with some of the French thinkers, and then of course Karl Marx shortly there after.
Marx himself saw early human society as a kind of communism, but his vision of pre-historic human society is basically the invention of the evolutionary community imagining what things must have been like.
For a good Catholic perspective on that, I recommend GK Chesterton's "Everlasting Man".
The point being, to speak of true communism apart from Karl Marx, is something like speaking of True Christianity apart from Paul.
Paul didn't make up Christianity, he didn't found it... but if you throw him out, you also throw out most of the New Testament, and what you have left isn't really Christianity anymore.