为什么美国作为一个移民国家却会产生强烈的反移民情绪?

aregalsonofabitch
I cannot answer your first question, but I can provide insights on the second.
The idea that America was built on multiculturalism appeared very early. By the 1780s, the term "melting together" was a widespread metaphor in use that was meant to positively portray incoming immigrants. Of course, America had just ousted a foreign power from their backs, so nationalism was running high. Hamilton, an immigrant from Nevis, argued vehemently against immigration, arguing that immigrants brought pro-monarchy and ethnic views that would undermine their new, fragile country. He also argued that America's bountiful resources and exploding population meant that America didn't need to rely on newcomers.

我不能回答你的第一个问题，但我可以就第二个问题提供一些见解。
美国建立在多元文化主义基础上的观点很早就出现了。
到18世纪80年代（1780年），“融合”一词已经成为一个广泛使用的正面性词语，用来描述即将来到美国的新移民。
当时，美国刚刚赶走了英国势力，因此民族主义极度高涨。
美国开国元勋之一，美国宪法的起草人之一的亚历山大·汉密尔顿，本人来自英属西印度群岛的尼维斯岛印度群岛，但他激烈地反对美国接纳新移民，他认为新移民会带来了亲君主制理念和种族主义观点，这将破坏他们刚刚建立的，脆弱的国家。汉密尔顿还认为，美国丰富的资源和激增的人口意味着美国不需要依赖新移民。

In the infancy of the country, with a boundless waste to people, it was politic to give a facility to naturalization; but our situation is now changed. It appears from the last census, that we have increased about one third in ten years; after allowing for what we have gained from abroad, it will be quite apparent that the natural progress of our own population is sufficiently rapid for strength, security.
At first, the two dominant parties of the time (Federalists and Democratic-Republicans) mostly agreed on keeping out immigrants. Thomas Jefferson wrote in his Notes on the State of Virginia in 1781 that foreigners would be anti-Democracy. However, by the turn of the 19th century, the Democratic-Republicans viewed pro-immigration policies as a great way to undermine the Federalists.

汉密尔顿认为，在国家刚刚起步时，由于人力资源的稀缺，放宽新移民入籍美国是一种策略，但现在美国的情况已经改变了。
从上一次人口普查来看，美国的人口在十年内增加了大约三分之一，很明显，美国人口的自然增长足够迅速，足以使我们获得力量和安全。
起初，占主导地位的两个美国政党(联邦党和民主党-共和党)大多同意将移民拒之门外。
对此，托马斯·杰斐逊在1781年的“弗吉尼亚州笔记”中写道，外国人不会认同美国的理念，他们都是反民主的。
然而，到了19世纪初，民主党人和共和党人为了削弱联邦党，转而支持接纳新移民

rumblith
The earliest exclusion and laws that occurred were focused mainly on the Chinese in the form of the Foreign Miners' Tax Act of 1850. The rise of this was due to the post gold rush economy.
Many of California's new gold rush prospectors arrived to find out there wasn't much in the way left for them to make their fortunes. So while the first arrivals didn't mind the Chinese when there was enough gold to go around for everyone--when it started to run dry, the resentment began to build. The Miners Tax ended up failing and led to the dying of Chinese gold camps which led to an influx of low cost Chinese laborers in cities.

美国对新移民的排斥最早主要集中在华人身上，其具体表现形式就是美国在1850年颁布的《外国矿工税法》。
当时，淘金热席卷美国，源源不断的新移民涌入加州，想要淘金发财，虽然第一批到达加州的人并不介意后来的华人加入淘金行动，但当金矿开始枯竭时，怨恨就开始逐渐积聚起来。金矿的枯竭导致华人劳工放弃矿工工作，转而涌入城市寻找工作。

Things got economically bad after 1877 and led to Chinese establishments being sacked and burned and Chinese being shot and hung. They saw that the Chinese had monopolized multiple manual labor industries like laundry, construction and landscaping for wages they couldn't beat and reacted poorly.
In 1882 the government passed the Chinese Exclusion Act that banned all Chinese immigration for ten years.
One of the common themes of these acts and laws that were passed is economic climate. In harsher times people seemed far more likely to lash out at those deemed different enough.
In the next two decades and in the early 1900's we started to see more of a rise of anti immigration sentiment towards southern and eastern European groups like the Catholics (Irish, Polish, Italians) as well as Jewish people though it would continue to increase after the great depression and around WW2.
Here's a random story about some Irish Orphans who weren't considered the right kind of white until they traveled across the country from NY to AZ to be adopted by Mexican-American families. That's when the fun happened and their white neighbors lost their minds at the sight of white babies adopted by Mexican-Americans.

1877年以后，美国经济形势变得糟糕，导致越来越多的华人居住区被洗劫和焚烧，许多华人被枪杀和绞死。
当美国本地居民看到华人垄断了洗衣、建筑和园林作业等多个体力劳动行业，而且获得了他们无法获得的高工资时，对华人的反应自然十分糟糕。
于是1882年，美国政府通过排华法案，在十年内禁止所有华人移民美国。
在接下来的20年里及20世纪初，美国本土居民开始对南欧，东欧，以及天主教徒(爱尔兰人，波兰人，意大利人)，犹太人的反移民情绪急速上升，这种情况在大萧条之后和二战前后依然存在。
举个例子，当时的美国有很多爱尔兰裔孤儿，由于爱尔兰裔一直处于白人鄙视链的底端，所以爱尔兰裔孤儿很少得到美国白人家庭的收养，于是一些爱尔兰裔孤儿在美国全境内流浪，另一些被墨西哥裔家庭收养。
然而，有趣的事情发生了，当白人邻居看到墨西哥裔美国人收养白人婴儿时，他们就会像被侮辱了一样，顿时失去理智。
（1848年大洋彼岸的美国加利福利亚发现了金矿，消息传到中国，饱受战争和贫穷折磨的中国人开始了美国淘金梦。此时的中国正是晚清最为贫弱、饥荒流行的时期，因此华人在国内越来越恶化的生存环境和美国工业化发展需求劳动力的双重作用下，开始大量向美国移民，很快在加州成了受剥削的廉价劳动力。华人移民主要是男性，大多当了矿工，忍受着与美国经济发展极不相称的低工资。
从表面上看，华人在美国19世纪中叶的大发展时期是受欢迎的,但种族歧视是无法逃避的。
因为淘金热时期成千上万的美国人从东部地区迁移到西部，而那时的美国东部盛行着反对欧洲移民的风气，因此那些从东部来的美国人也带有浓厚的本土主义态度，反对外来移民。
而那些白人新移民，如爱尔兰人、俄国人，在遭受了美国东部本土主义的歧视后发现，在攻击华人移民的同时，可以使他们自己的地位得到提升。而处于社会下层的美国矿工也把工作刻苦、甘愿拿低工资的华人劳工视为导致自己工资下降的罪魁祸首。
美国排华有一一个从民间到政府、从地方到全国的发展过程。排华源于加利福尼亚金矿区，
随着华人迁入城市而扩展到其它行业，从加州发展到中西部地区,最终形成全国性问题。在50年代和160年代，反华骚乱还是零星的个别现象,到70年代中期则发展为大规模的、集中且有组织的排华运动。排华主要有两股力量。一是来自民间,通常采取的方式是不经过任何法律程序的暴力行动,如驱逐、殴打，甚至杀害华人,抢劫、焚烧华人财物，造成一种恐怖气氛。这股排华力量以美国本地劳工为主，并与劳工运动相结合，形成政治压力迫使美国政客和政党作出反应。
第二股力量来自美国政府,美国政党和政客出于选举的考虑，不惜牺牲华人，默许民间排华。故而地方当局、州及联邦政府相继制订歧视、限制华人的法律,阻止华人进入美国。这两股力量互相影响配合，促使美国国会在1882年通过排华法案并使排华成为美国的国策。80年代中期,在美国太平洋沿岸诸州又发生了一系列暴力排华惨案，最著名的如1871年的洛杉基惨案、旧金山骚乱和石泉大屠杀等。
此后，排华主要转向政府层面，由美国政府制订措施来限制中国移民。到1904年，美国国会立法完全禁止华工赴美。其中，随着时间的推移，美国各州和联邦政府分三步骤制定和贯彻排华法。
首先，是剥夺华人的公平竞争权。然后是限制华人移民。最后的是排斥华人归籍。加州正是按照这样的模式，步步的实现其排华构想，而美国联邦政府则是继承了加州的经验后直接跨越到第二阶段，以至最终将排斥华人入籍作为其立法、司法和执法的主旋律。）

JustZisGuy
Follow-up question: at the time of the American Revolution, was there a social distinction between recent immigrants to the colonies compared to those having been there much longer (say, descendants of early Virginia Company or Plymouth/Massachusetts Bay Colony settlers)? In other words, was there a distinction between "locals" and "the British"?

在美国独立战争时期，新移民到美国的英国人，和更早在美国定居的英国人(比如早期居住在弗吉尼亚公司或普利茅斯/马萨诸塞州殖民地的英国人)相比，是否存在社会差异?
换句话说，美国“本地人（其实祖上也是英国人）”和后来的新英国移民之间有区别吗?

Kayra2
America didn’t really start off as an Immigrant country. The first colonies that were formed at Virginia and Massachusetts were formed in 1607 and 1620 respectively. Given that the modern-day USA was born in 1776, that’s 156 years of life in the continent, and enough for your grandchildren to naturalize in any country by today’s standards.

美国一开始并不是移民国家。
英国分别于1607年和1620年，在北美弗吉尼亚州和马萨诸塞州建立了第一批殖民地。
考虑到今天的美国于1776年才正式建国，所以在美国建国前，从英国来的移民已经在美洲大陆上生活了156年了，按照今天的标准，这么长的时间足够让你孙子的孙子在任何国家入籍了。

These original colonists didn’t come here for no reason at all though. Catholicism was restricting freedoms throughout Europe and some immigrants came to escape this religious persecution to practice Puritanism (This is a completely different subject that requires a different research). Most of them came as indentured servants, slaves for pay for a predetermined amount of time, because the price to sail was too steep. These servants ranged from white Europeans to black West Africans. By the time of the Civil War, there were a continuous influx of people from across the Atlantic to the states, which all came either as slaves or indentured servants from all walks of life.
All the way until the declaration of independence and the civil war, the US was known in the world as a place with “class mobility”, where you can work your way into the upper class and become rich and elite. The US promised freedom to practice your own religion, your own language.

最早的一批移民并不是无缘无故来到美洲大陆的。
在当时，天主教限制了整个欧洲的自由，一些清教徒为了逃避宗教迫害而坐船前往美洲。他们中的大多数人都是契约仆役。这些仆役从欧洲白人到西非黑人不等。到南北战争时，仍然不断有大批的人从大西洋彼岸涌入美国，这些人要么是奴隶，要么是各行各业的契约仆役。
直到美国内战之前，美国一直以“阶级流动性”而闻名于世，在当时的美国，你可以通过努力进入上层社会，成为富人和精英。美国保证民众自由信仰自己的宗教，使用自己的语言。

Shipment of people to the states were around 60000 for more than 50 years until the famine in Ireland and political turmoil in Germany, which boosted these numbers dramatically. In 1851, there were 380000 people in the US ports of entry, a very dramatic increase in the consistent influx of humans. 2.7 million new prospective citizens entered the country in the next 7 years, and most of these people were Catholic in a time where Catholicism was hated in the US. There were stark opposition to Catholic churches and schools, but these immigrants had bigger problems. They drew hostility because of the diseases they brought with them from the old world. They were poor, just like the original immigrants but instead of improving the forests of Massachusetts into a sprawling city, they diminished its features with the slum housing they stayed in, the increase in crime rates, alcoholism and other misdemeanors.

自美国独立后的50多年里，每年向美国输入的移民数量大约在6万人左右，直到爱尔兰发生饥荒和德国发生政治动荡，移民数量才大幅增加。
仅1851年，就有38万人通过美国入境口岸，随后美国移民数量急剧增加。在接下来的7年里，有270万新移民进入美国，其中大多数人都是天主教徒，而在当时，天主教在美国是不受欢迎的。
新移民在美国建立的天主教会和天主学校遭到了当地人的强烈反对。就像最初来到美洲大陆的移民一样，新移民带着疾病与贫穷来到美国，他们没有给城市带来繁荣，反而聚集起来，形成了贫民窟、凡是有新移民存在的地方，就会出现犯罪和酗酒。
在美国出生的新教徒认为，他们这些奉行英国传统文化的人，才能代表真正的美国精神，因此他们很鄙视爱尔兰人和德国人。

So to finally answer your question, anti-immigration sentiment arose from immigrants themselves because they viewed new immigrants as fundamentally different from themselves or their families. America undoubtedly was a melting pot, but this did not exclude people from making the distinction between cultures. Blacks were slaves, Irish were poor, Brits were true Americans etc. and anti-immigration is a very broad term for everyone who came to the US. Given all of these distinctions,

最后回答你的问题，反移民情绪来自于移民本身，因为他们认为新移民与他们自己或他们的家庭存在巨大差异。
毫无疑问，美国是一个大熔炉，但这并不能阻止人们自发对不同文化进行区分。
不同的美国群体对移民有不同的标签，比如，黑人是奴隶，爱尔兰人是穷人，只有英国移民后裔才是真正的美国人等等。