In the over-hyped world of talk radio (both on the left and right) demonizing your opponent is the way of the world. Actually listening, showing the fruit of the Spirit, demonstrating love is not. So initially, looking beyond the fact that such a conflation is laughable, I will do what Mr. Beck doesn't do for me (as an advocate of biblically motivated social justice): I'll take him seriously.
Here is the biblical argument for social justice. All men are both created in the image of God (ie. imago dei) and all are depraved (broken in sin). As such, all men are capable of creating great things (work, organizations, systems, rules, art, etc..) yet are incapable of creating anything that does not reflect human brokenness in some way. When we create systems, organizations and societies, none of them will be fully righteous (ie. just). . . because in the Reformational understanding of sin. . . every part of our being and work is affected by the fall. (we are not as bad as we could be, but every part of us does reflect our sin).
Personal unrighteousness (sin) is any violation of our covenant to live as we should before our God ("should" is always defined by properly reflecting God's character). But the things we create (including systems, corporations, societies, nations and more) also are capable of violating the covenant calling to always reflect God's character. In the US we routinely assume that God always deals withs us as individuals and never corporately, yet throughout the scripture we see nations and groups of people indicted for their neglect of the ways of God. Any violation by a society of the ways of God (including caring for those who are weak, broken, marginalized, cheated, young, old, fatherless, etc..) is a violation of God's righteousness (justice).
Social Justice would be anything in which a nation, society or group of people abide by the covenant to reflect God's character in truth. This is a far cry for arguing that the means of production should be held by the state and distributed "evenly" among all people (as if this were possible).
World-formative Christianity (in the descriptive words of Nicolas Wolterstorff) suggests that as Christians we are called to reform not only our lives to be in keeping with the character of God, but our societies, institutions, systems, organizations and more. That is the call of social justice.
Biblical Christianity, and this world-formative stuff, is not actually ever about being sure people lose their ability to creatively, freely, magnify the God of the universe through work and reformation. And, it is never about bringing "equality" of the socialism type, but it does challenge us to ask what it means to have enough?