There are two issues here that I see with Liberation theology. The first being that priests and religious should not be engaged in war, the second is the materialism that is thoroughly mixed up in liberation theology.
Priests are images of Christ, who wished to save all men, including His enemies. Thus, he never killed, as this shortens the time we have for conversion. While there may be instances when priest should fight, and certainly instances where they should protest, preach against government action, etc, their primary purpose is to save souls, and to provide the sacraments, since laymen cannot do the latter. Compare priests who prioritize fighting for rights over prayer and providing the sacraments to those military chaplains who would not pick up a gun, but died giving the last rites to soldiers, friend and enemy.
The other problem with liberation theology, is not that it encourages self-defense over oppressive Catholic-hating governments. Many Christeros are up for sainthood, and they did fight. Liberation theology, however, as with fighting priests, emphasizes being comfortable in this life almost to the exclusion of being saved in the next. Catholics believe in redemptive suffering, we do not think it is evil to suffer. While it is evil to inflict suffering, we believe suffering, when embraced, unites us to Christ and is a special form of prayer, a powerful way to love.
Materialism is rampant, and has been for some time. It is present in communism and liberation theology as well as the secularism and consumerism of the west. Many popes, including John Paul II through Francis, have warned against it in each of these settings.
If you are interested in learning more about the Church’s social teaching, the Vatican organization on doctrine has also come out with a Compendium on the Social Doctrine of the Church, which is unfortunately as lengthy as it sounds. However, it has a decent index to narrow down to what you’re looking for. I would also suggest reading some of the enciclicals about it, such as Rerum novarum, Quod apostolici muneris, Quadragesimo anno, or some of the popes’ addresses on liberation theology.