What is wrong with capitalism is simply that it is based on human antagonism, and it is precisely here that it comes in conflict with Christianity. Capitalism is a state of war, but not just a state of war between equivalent forces; it involves a war between those who believe in and prosecute war as a way of life, as an economy, and those who do not.Herbert McCabe OP, "The class struggle and Christian love", God Matters, p. 193.
Christianity is deeply subversive of capitalism precisely because it announces the improbable possibility that men might live together without war; neither by domination nor by antagonism but by unity in love. It announces this, of course, primarily as a future and nearly miraculous possibility and certainly not as an established fact; Christians are not under the illusion that mankind is sinless or that sin is easily overcome, but they believe that it will be overcome. It was for this reason that Jesus was executed - as a political threat. Not because he was a political activist; he was not. ... Certainly Jesus was not any kind of socialist - how could anyone be a socialist before capitalism had come into existence? But he was nonetheless executed as a political threat because the gospel he preached - that the Father loves us and therefore, in spite of all the evidence to the contrary, we are able to love one another and stake the meaning of our lives on this - cut at the root of the antagonistic society in which he still lives.
Christianity is not an ideal theory, it is a praxis, a particular kind of challenge to the world.
McCabe's mention of the possibility of living together in love as a "future and nearly miraculous possibility" brought to mind Rob Bell's discussion of heaven. (Not that Rob Bell and Herbert McCabe agree politically. McCabe is a socialist. I'd be surprised if Bell is. Though don't tell John Piper or Justin Taylor about this post or that'll be the next controversy.) Eternal life is the life of the age to come. That age that is often described by the prophets in this-wordly ways using words like justice and peace. We are called to live the life of the age to come in this present age, to pull the future into the present. In this way we are to be imitators of Jesus, who not only exemplified this but brought about its possibility by his ministry.
I do not mean to imply that the life of the age to come means participating in the class struggle. Neither do I mean to deny it. I just made the connection as I read McCabe this morning and thought I'd pass it on.