Liberation Theology is a phenomenon of the Catholic Church. I understand the Pope John Paul II has had some rather harsh things to say concerning this theology. The largest supporters have been in Central and South America. With respect to Socialism, Pius XI in Quadragesimo Anno(1931), stated, "Socialism, entirely ignorant of and unconcerned about the sublime end of both individuals and of society, affirms that human society was instituted merely for the sake of material well-being." Paul VI expressly condemned four principles of Marxist ideology which a Christian could not hold in Octogesima Adveniens(1971).
From the Protestant perspective, you are referring to the phenomenon characterized as the "Social Gospel". That it is thoroughly pervasive in Protestantism is not evident. However, that it characterizes the theology of a number of "mainstream" Protestant denominations is a reality.
A number of people in my family are prominent Presbyterian theologists and administrators. They are typical, aging, Berkeley, Marin, and Palo Alto liberals living off old money. These folks milk their congregations for money while they soft-sell the agenda.