Maybe others have already answered this, but let me blunder on ahead anyway.
Our (that is, Catholic) thought is not as centered on “rights” theory as on two strands of thinking that we weave together. One is the OT theme that justice includes generosity and solicitude for the needy. The other is the notion that (a) justice is “rendering what is due”; and (b) the needy, by virtue of being human, are ‘due’ assistance. All this lives under the heading “solidarity.”
Lest this sound like “from each according to his ability, to each according to his need,” the other ‘pole’ of Catholic social thought is “subsidiarity.” This means that while the hungry infant is ‘due’ nourishment, the people who ought to provide it are his family. If they can’t, then the neighborhood, the village, then the county, then the state ... and so forth.
The countries south of the Rio Grande bear a great shame because they have ducked their responsibility. Because mercy is a duty, we bear SOME obligation to care for those they neglect — but not in a way which cripples our own nation or which relieves rich Mexicans from their shame.