Capitalism Assumes people are basically selfish and will work hardest to benefit themselves and pass their neighbors by.
God tells us that we are ALL selfish by nature. Thus communism goes against the Christian principle of man's nature being sinful(selfish). Capitalism is the system that would be most likely to work best if God is correct about our selfish nature. Therefore only a foolish Christian would expect an altruistic system to work on large groups of people exercising their natural preferences outside of God's constant intervention. The story of Annanias and Sapphira illustrates how two people naturally chose to lie about their property rather than be altruistic while claiming to be altruistic even though they were holding back some of their property from the altruistic sharing. Needless to say communism will always need heavy handed enforcement to force people to comply against their nature.
Yes, absolute power corrupts absolutely. This is the root of Communism. And it is wrong.
But to club Communism with Atheism, and mix arguments, will convince none.
Selfishness is recognised in all religions, by the way, since the dawn of time.