Jesuit priest James Martin attempts to put a small dent in Glenn Beck's vast ignorance on the subject of liberation theology in an essay at the Huffington Post:
Liberation theology began in Latin America in the 1950s and 1960s, and was later developed more systematically by Catholic theologians who reflected on experiences of the poor there. The term was coined by the Rev. Gustavo Gutierrez, a Peruvian priest, in his landmark book A Theology of Liberation, published in 1971. Briefly put, liberation theology (there are many definitions, by the way) is a Gospel-based critique of the world through the eyes of the poor. Contrary to what Beck implies, the liberation theologian doesn't see himself or herself as victim; rather proponents call us to see how the poor are marginalized by society, to work among them, to advocate on their behalf, and to help them advocate for themselves. It has nothing to do with seeing yourself as victim. It is, like all authentic Christian practices, "other-directed."
It also sees the figure of Jesus Christ as the "liberator," who frees people from bondage and slavery of all kinds. So, as he does in the Gospels, Christ not only frees people from sin and illness, Christ also desires to free our fellow human beings from the social structures that keep them impoverished. This is this kind of "liberation" that is held out. Liberation theologians meditate on Gospel stories that show Christ upending the social structures of the day, in order to bring more--uh oh--social justice into the world. Christians are also asked to make, as the saying goes, a "preferential option for the poor."
It's not hard to see what Beck has against "liberation theology." It's the same reason people are often against "social justice." Both ideas ask us to consider the plight of the poor. And that's disturbing. Some liberation theologians even consider the poor to be privileged carriers of God's grace. In his book The True Church and the Poor, Jon Sobrino, a Jesuit theologian wrote, "The poor are accepted as constituting the primary recipients of the Good News and, therefore, as having an inherent capacity of understanding it better than anyone else." That's pretty threatening for any comfortable Christian. For not only do we have to help the poor, not only do we have to advocate on their behalf, we also have to see them as perhaps understanding God better than we do.