Yeah, why not. The us was a christian protestant ethnoestate for like 200 years, and in the cathecism of the catholic church it says that a country altought it should welcome foreigners to the extend they are able, it may restrict inmigration.
If you make the case that a nation is a bunch of people that descend from a certain group, you can make the case to restrict inmigration to preserve the ethnic group. And that they are only able to accept in a limited number of foreigners at a time to avoid changuing the demographics, because if the demographics changue and the original ethnic group dissapears , the nation would die off.
If youre French, and one of your great-grandparents are Italian, that making you 1/8th italian, you would still be considered French by most, if not everyone.
But if you were only 1/4 french and the rest were to be a mix of other ethnicities you probably wouldn't.
Its easy to make an argument of why a country may need to restrict inmigration for its own good, this being just the ethnic nationalist argument (you could make an economic argument as well)
You can also argue that one has different degrees of duty towards different people based on their relations and their proximity to them
A man is to put first her wife to her parents, a man is to specially care about his family.
There is a thing called Ordo Amoris, that influenctial churchmen santified by the church established, in which a man is to care first about god, then family, then nation, then the rest of the world
One thing you should take into account is that this kind of massive inmigration from countries so different both racially and culturally foreign to us is something kind of new, so there isn't much doctrine written about it.
Moreover, most of the clergy are older men that haven't grown up being a minority in the school of their own nation so they don't realize how bad things really are.
Younger clergy , that typicallt has less power increasingly against inmigration, so in a few decades they might oppose it more.
