Now Cardinal Ratzinger is Pope Benedict XVI, and when he arrives here on Wednesday for his first pastoral visit to Latin America he may be surprised at what he finds. Liberation theology, which he once called “a fundamental threat to the faith of the church,” persists as an active, even defiant force in Latin America, home to nearly half the world’s one billion Roman Catholics.

Over the past 25 years, even as the Vatican moved to silence the clerical theorists of liberation theology and the church fortified its conservative hierarchy, the social and economic ills the movement highlighted have worsened. In recent years, the politics of the ...