Spyman: The essential difference being that neither capitalism or communism claims divine mandate.
Or really any moral truth. Particularly capitalism. Its an economic system, not a system of morality (I would make the assertion that even people who are gung-ho capitalists would concede that capitalism isn't moral or immoral, but amoral.) I wouldn't want to put words in Putin33's mouth, but I'd hazard a guess myself that communism makes claim to be a source of morals, merely a system to get more equality and justice.
Religions in general make the claim for being the font of morality. That is but one of the issues I have with the concept.
That, and the body count that supposedly God racked up back in the day. At least the Greeks had the decency to make their gods openly petty and generally bastardous. Zeus killing a motherfucker isn't a shock, because Zeus was, according to the myths, a giant asshole.
Yahweh, God, etc is set up as a perfectly moral and perfectly good being. Yet, he supposedly condoned massacres, slaughter, etc.
God wills it, after all.
Its the blatant contradictions and hypocrisy that really make Christianity annoying.