This is the result of Liberation Theology and the Social Gospel. People were taught that socialism is the Christian thing to do...and they believed it. Now they can’t separate their leftist politics from their faith.
Until the 1972 election, Catholics had either never voted republican, or had once in 1956 (depending on the source), today’s Catholic vote is the best that it has ever been, and winning 48% of the Catholic vote in 2012 is a pretty good year for republicans and Catholics, in fact, one of the best in history.