I think it's wise for us Catholics to start with the Catechism:
2241 The more prosperous nations are obliged, to the extent they are able, to welcome the foreigner in search of the security and the means of livelihood which he cannot find in his country of origin. Public authorities should see to it that the natural right is respected that places a guest under the protection of those who receive him.
Political authorities, for the sake of the common good for which they are responsible, may make the exercise of the right to immigrate subject to various juridical conditions, especially with regard to the immigrants' duties toward their country of adoption. Immigrants are obliged to respect with gratitude the material and spiritual heritage of the country that receives them, to obey its laws and to assist in carrying civic burdens.
And then we should also consider Pope Francis' recent words:
In St. Peter’s Square, the pope told a Sunday gathering that it was not enough to merely sympathize with those brought to Europe’s shores by convulsions of war and hardship.
“May every parish, every religious community, every monastery, every sanctuary of Europe, take in one family,” the pope said, according to Vatican Radio. He added that the Vatican would take in two families.
“The Gospel calls us to be close to the smallest, and to those who have been abandoned,” the pontiff said.
Taken together, these things mean that Catholics really can't just turn our backs on this matter, or insist that the refugees be kept quasi-permanently in tent cities, or otherwise remain unmoved by their plight. What exactly we can do will depend on many things, including the United States' political decisions regarding whether any more people from these stricken areas may enter our country. Mindfulness in prayer and thoughtful donations to the appropriate charities who are helping these people should be among those things many of us can do.
Unfortunately I'm seeing a lot of highly negative comments and opinions by various observers, some of whom are Catholic, who seem to think some rather odd things. Some seem to think, for instance, that it is perfectly acceptable for Catholics to refuse to help or to bar the way to any but Christian immigrants. Others would counsel a policy of refusal on the grounds that letting Syrians and others into Europe will destroy European culture. Still others have veered into outright xenophobia or racism.
Neither the Catechism of the Catholic Church nor anyone else says that no one is allowed to make prudent choices regarding specific types of aid offered to specific groups of immigrants. But if I may borrow from Mark Shea's formulation during the endless torture debates, the question here for Catholics ought to be, "How should I welcome the stranger?" not "How can I tiptoe right up to the line of indifference or outright hostility to the stranger without actually crossing that line?"
Now, "How can I welcome the stranger?" is a question that may indeed be framed by legitimate practical considerations. If, for instance, a specific Catholic parish in Europe, mindful of the pope's call but unable to act on it owing to local laws prohibiting the actual physical taking in of a refugee family, regretfully determines that they are unable to extend this particular form of help, but instead raises a collection to send to a parish somewhere else that is able to take in a family or two--that is fine. If a group of lay Catholics in Germany decides that they wish to establish a humanitarian fund that will help Syrians who wish to do so to remain in or nearer to Syria instead of migrating, that, too, is fine (again, provided it is permissible by appropriate laws). The focus on welcoming the stranger and helping the oppressed is not dimmed by trying to do so creatively and well.
But "How can I tiptoe right up to the line of indifference or outright hostility to the stranger without actually crossing that line?" is not a legitimate moral question. It seeks to continue to think of the migrant or refugee as an object instead of a person--and an object, sadly, for derision or contempt or full-blown hatred. Such are the attitudes of those who see in the faces of weary families only terrorists or Muslims or the Other; such are the words of those whose fear of these people would remain if only a thousand, or only five thousand, were coming.
Again and again in the Gospels Christ makes it clear: there are no Others. There are no strangers. There are only neighbors. And how we treat our neighbors in situations like these reveals more about our faithful discipleship to Him than we may realize.