refer to St Thomas Aquinas on immigration...according to the Saint, one requirement is that the immigrant not change the existing culture. Certain basic beliefs must be the same. Prior immigrants from Italy, Poland, France, etc were from countries/cultures that understood Christendom (granted, often honored in the breach)
Mazza La Ragazza shares this
If more Americans, including non-Catholics, knew what St. Thomas taught, we would have fewer problems than we do now.