In short, by most criteria set by Americans themselves, immigrants are more useful citizens than they are.
Buit if they are not white, a lot of white Americans start to get uneasy, and ask questions about assimilability. Many Americans look back nostalgically to the relatively ethnically homogeneous '50s. They're uncomfortable with a multicultural USA, as are many Germans. And as are many Norwegians.
Average people are a lot more average and I think I've produced a decent argument that they have something to fear from immigration. People like us know that immigration is good for the economy and our differences around here are almost wholly on which immigrants should come in and under what terms.
But we gain from a general increase in wealth and are smart enough to know that an 0.5% increase in GDP is something hugely worth having.
The "economy" is an abstraction. For example, a US company may sack a lot of its American coders, and hire Indians in their stead. The bottom line of the company may improve; it may become more "efficient" as a result; and in such manner it might be argued that the "economy" is "better." But that is scant consolation for the sacked coders, or those forced to take jobs with lower wages and benefits. Or even the employed coders, who find that a new labor reserve of coders is undermining their own pay increases and conditions of work. The winners seem to be the owners on top.
And the use of immigrant labor to undermine domestic labor is nothing new in American history.
But imagine the sort of person who has rarely left his state and never left the USA, scraped graduation from high school, who thinks nitrogen is a poison gas, watches Fox news and works in a near minimum wage job. That's a good % of the US population.
But thirty or forty years ago he might have got a unionised factory job, and one that offered some apprenticeship or training program. Now he's the vistim of a dysfunctional school system, stuck in a dead-end minimum-wage service-sector job and can't afford to get credentialed as it costs an arm and a leg -- with no guarantee of payback at the end. In some dim manner he senses that outsourcing, deindustrialisation, the evaporation of good jobs, unfettered immigration, "free trade," and the resulting disparities in wealth and income are tied together..
He has a job, but only just and like far too many Americans far too few portable skills to get another.
Which may not be his fault. Unlike Nordic Europe, getting portable skills can cost an arm and a leg.
You say to him that immigration curbs will knock 0.5% off GDP, he will think that's a good deal, since he will feel that he has a >0.5% chance of losing his job. Objectively, that's not entirely irrational.
Particularly when that 0.5% will come from the overflowing coffers of the rich.
This is why there is an American political movement against "the elite" which as far as I know exists nowhere else, and the only historical example would appear to be the Chinese cultural revolution.
The populist right (Limbaugh, Coulter, etc.) -- fed by the rich (Koch, etc.) -- tries to make people think that DC is controlled by the "liberals," who are supposedly a bunch of multi-culti, metrosexuals whose tastes run to literature and art. Disinformation, propaganda, and false consciousness. It is channeling people's genuine grievances and apprehensions into useless directions. This feeds into a long-time distrust and dislike of intellectuals (which Tocqueville noticed two centuries ago). It also feeds into a dislike and distrust of centralised federal government, particularly in the South, which has often been loud-spoken about "states' rights." These people have never forgotten the Civil War. All of these are undercurrents in American social and political life -- but they can't be sensed in a place like NYC (for instance).
