Just as it has been in the past, this is about opening the doors for more Roman Catholics. He would not be calling for it if the nations south of the border were overwhelmingly Protestant.
It is that but more so the Jesuits particularly and much of the Catholic church are infected by liberation theology and marxism to the point of no return. It is about destroying national sovereignty to aid bringing about world socialism and world government. For the same reason the Catholic church would support the FSLN in Nicaragua to the point of allowing the Pope to visit where he was lucky to not have been killed on the spot. Ideologically many can’t help themselves even if the outcome is anti-Christian and suicidal.