Cardiff Garcia brings us the 1864 Republican Party platform on immigration: "Resolved, That foreign immigration, which in the past has added so much to the wealth, development of resources and increase of power to the nation, the asylum of the oppressed of all nations, should be fostered and encouraged by a liberal and just policy."
Today obviously they're striking a different tune as do many voters. But I do think that if you think about 19th Century America basically everyone sees it in retrospect the way the GOP saw it back then. Here you had this great big country with lots of natural resources and a bold new experiment in representative government and what you needed to add to the mix was more people so the land could be productive and we could build factories and so on and so forth. And what's interesting is that in the case of internal migration, people seem to see that. Thirty years ago there were 1.1 million fewer people in New York City than there are today, and to the best of my knowledge this is universally regarded as part and parcel of the city's revival. It's not that conditions got better in the city and then a bunch of folks showed up to "take jobs" from native-born New Yorkers. The economy is made of people, and the people moving into the city is what what the economic revival consists of.
Or you could think about it in terms of transportation infrastructure. If a new freeway spur gets built out to a town, nobody says "more people will move here thanks to improved transportation access and joblessness will skyrocket." If more people move to town, that means more investment in residential and commercial structures and more employment in the locally focused services (health, education, retail, food service) that provide most of the employment.
Now obviously this isn't a totally universal principle. If a serial killer moves to town, that's bad news. But a law-abiding person who's come to town to do a job? That's a good thing, unless he's specifically competing with your exact set of skills. Fostering and encouraging the migration of a diverse set of people with diverse skills and aptitudes is only going to add to the wealth and power of the nation.