Many Christians were members of the Communist Party until the Church made that membership an excommunicable offense. We ought to remember that some of the core values of communist theology come from the Bible: For instance; “From each according to his abilities, and to each according to his needs.”
It isn’t clear to me that communism has a “theology.” Nevertheless, I think your point may add some insight into why communism has become synonymous with atheism. I.e., that communists generally have been atheists, not that atheists generally have been communists.
It is true that “From each according to his abilities, and to each according to his needs,” seems to have been characteristic of the early Church, but how was that general outlook different from communism?
It might be observed that communism is a political ideology, one that seeks to impose “From each according to his abilities, and to each according to his needs,” upon citizens by decree of the law. The early Church was entirely voluntary which, I suppose, changes the very nature of the belief for each .
Where does atheism come in?
Suppose an atheist were to subscribe to “From each according to his abilities, and to each according to his needs,” as the most important moral principle. Further suppose that atheist has political interest in bringing about the most moral society they can imagine. Given a lack of belief in the supreme being, the atheist’s only recourse to realizing his ideal of utopia on earth would be by political fiat.
A theist, on the other hand, with a more sober and realistic understanding of human nature and sin, knows better than to think human beings will subscribe to “From each according to his abilities, and to each according to his needs” freely and the likelihood of making that ideal a reality without the application of a great deal of political force being imposed (along with many deaths and lots of suffering) is basically zero. Given the theist’s understanding of human nature and sin, the theist will patiently leave the bringing about the kingdom of heaven on earth to the grace of God and the true conversion of sinners, not to political regimes and brute force.
Humanitarian atheists with a strong predilection to the realization of the idea of utopia will necessarily rely upon the only means left to them – politics – to embody what they have decided is their supreme principle, “From each according to his abilities, and to each according to his needs.” They will then turn to political activism and, frustrated by their incapacity to change hearts, will ramp up the use of force to impose that principle by any means necessary – BAMN (if you get the reference.) Full throttled communism, here we come.
Or, put another way:
idealism + atheism = communism