It is sad and ironic that I, a communist, find myself defending capitalist economics against Libertarians. I, an atheist, might as well be defending liberal Christianity against the fundamentalists.
The difference is, of course, that there is at least some truth to capitalist economics. Not much, I concede, but some truth nonetheless. And it's a shorter step to communism from modern capitalist economics, especially Keynesian economics, than it is from Libertarian laissez faire economics. The latter is almost completely delusional.