This was very true in the distant past, of course, sometimes their presence was believed to be more even more insidious, especially the Italians, at times. Below is mostly from the ebook I penned a few years ago, From the Antipasto to the Zabaglione – The Story of Italian Restaurants in America:
The prominent mid-century historian Richard Hofstatder posited about the mood of much of the general public soon after the First World War: "The Anglo-Saxon Americans now felt themselves more than ever to be the representatives of a threatened purity of race and ideals, a threatened Protestantism, and even a threatened integrity of national allegiance – for the war and its aftermath had awakened them to the realization that the country was full of naturalized citizens still intensely concerned with the politics and divided in their loyalties.” This was the time of the dramatic rise of the Ku Klux Klan when, "the Catholics were the primary objects of their resentment, at least outside the South,"and another reason of widespread anti-Italian sentiment, as these Italians were nearly all Catholic.
Xenophobia against many of the newcomers was even reflected in scholarly quarters. Edward Alsworth Ross, Professor of Sociology at the University of Wisconsin – and a founder of American sociology (muse on that after finishing this sentence) and President of the American Sociological Society in 1914-1915 – wrote in a trade book about immigration in 1914 that unless the flood of “gross little aliens” from “the backward and benighted provinces from Naples to Sicily” was sharply diminished, America, “must in the end resign itself to lower efficiency, to less democracy, or to both.”
These views were held widely enough for two pieces of legislation restricting the tide of immigration from Italy. The Quota Act of 1921 limited its immigration to 3% annually of their population in the 1910 census. The Johnson-Reed Act in 1924 further reduced the new arrivals from southern and eastern Europe to 2% of the 1890 census. Immigration from Italy had slowed to a trickle when the First World War reached it furious conclusion as Germany exhausted itself and the even deadlier influenza epidemic beginning in 1918 infected a fifth of the world's population and killed around 50 million people. The pace of newcomers from Italy increased in 1920 and reached a last peak of 220,000 in 1921 before declining to around 50,000 per annum for a few years before the quotas took full effect. There were just 6,000 immigrants from Italy in 1925. The number averaged 15,000 for several years afterwards, a far cry from before. This was not changed until the large-scale immigration overhaul in 1965. This set the stage for current restaurant dining diversity that exists today.
And, very truthfully, as the President followed that initial sentence above: "America wasn’t weakened by the presence of these newcomers; they embraced this nation’s creed, and it was strengthened." Even concerning the Irish....