If you mean the religious left is confined to explicitly socialist religious peoples, that's a small group. Catholic Workers, Jim Wallis-Soujourners types. But the religious activists I have known generally reject what they describe as materialism (greed), competitiveness, and accept what most Marxists would regard as a standard if somewhat superficial--and not always superficial, cf Penny Lernoux, if anyone remembers her--analysis of capitalism. I don't mean, the labor theory of value, but rather the general idea that the world exconomy runs on exploitation and injustice and can't fixed by merely ameliorating these. I would say that most so-called socialist activists I know,a s opposed to theorists, operate on ther same wavelength.
I should note taht even rather conservative versions of Christianity sometimes have an articulated critique of capitalism. Catholicism is a case in point.
--jks