You're equating "Anglo-Saxon" with "white" here, but they mean different things. Compared to its rivals at the time, the U.S. from its founding through 1925 was more open and diverse. It restricted naturalization to mostly white people - but at the time, "white" included a wide range of non-Anglo-Saxon ethnicities from Irish to Mexicans to Italians to Jews to Russians and more. Also, the initial population of the colonies was only around 80% white. These made it significantly more diverse than its European rivals. From 1925 to 1965, there was a much more restricted immigration policy - especially as a pushback against non-Anglo-Saxon immigrants like Irish, Italians, and Jews. However, that was a limited period and immigration opened up further after that.
Our diversity has never been perfect - but it gave us gospel and jazz and rock 'n roll. It made us the leader in atomic energy thanks to Jewish and other non-Anglo-Saxon immigrants. It has generated much of our uniquely American cultures and traditions.
It also gave them slavery, riots, segregation, affirmative action, no child left behind, gangs & mafias, BLM, statues torn down... I think it's just cherrypicking. When diversity works out, it's great and civic nationalism gets credit. When it doesn't, everybody looks the other way and blame it on the left. And even then, jazz and gospel are distinctly black; they come from mostly black artists who gathered in black communities. They formed subcultures; not diverse at all. Throughout history, they had hundreds of ghettos and hyphenated Americans; how is that unity?
The question is, what is considered "forced" in terms of immigration? For example, I would say that the whites-only naturalization is just as forced and political as any other immigration laws. I don't think there is a neutral choice. Immigration will always reflect our values and politics. The Immigration Act of 1965 was voted in by a strong majority of both parties who were democratically elected. The changeover from whites-only naturalization to modern immigration reflected the will of the American people as a whole, not just politicians.
I doubt the 1965 naturalization represented Americans; Why did they change their policy all of a sudden? What prompted them to go from segregated schools and whites-only to opening their country to practically anyone? To this day, people still oppose immigration; it's one of the most controversial issues. Imagine back in the 60's.
(1) There is no ideal ratio. There are countries that are more diverse and countries that are less diverse, and both make it work.
(2) Migrants have never left their identity behind, nor has there ever been perfect agreement between Italian-Americans, Irish-Americans, and English-Americans. They can still live in peace and cooperate despite their differences, though.
(3) Diversity isn't required as I said, but America became great - among other things - by being more diverse than its rivals in Europe.
(4) I like to have some people of similar background, but it doesn't need to be a majority. I like the diversity of most of the places I've lived - all within the U.S. but in mixed communities. Currently, my church is mostly white and I'm fine with that. My workplace is mostly Asian, and I'm fine with that as well.
(5) I don't see a problem with that if it happens peacefully from democratic will. My father married my mother, who is white. I have one cousin who married a Chinese woman, and another who adopted Chinese children. It has worked out well for us, and I would be fine if the rest of Korea were to have similar experiences as my family.
America had a good economic policy, constitutionalist values, immigration of hard-working people, and benefitted from both world wars. Having different ethnicities didn't bring any of those things about. What I don't get is why you go from saying "diversity made us great" to "diversity is not necesary". How would you know if diversity caused the greatness of America? You're now more diverse than ever before, yet people feel discontent because of this. If diversity is such a source of greatness, why do people demand less everywhere it happens; Europe, America, Asia, Middle East, etc.?
Why do you prefer to be around other Asians? I think that proves my point exactly. People still flock to their own, based on cultural background and ethinicities, and there is no such thing as Americans being united by common constitutionalist values.
Eventually, when whites become a minority in America, do you think they will be treated with the same kindness they offered other minorities? Or will they become the scapegoat and denied rights? Will the constitutionalist values remain, or will they be replaced by the values and sensibilities of other demographics who value identity politics more than free speech and fiscal conservatism? Do you think the people who are migrating now to America care about preserving the constitution, free market meritocracy and a republic? Or will they vote in their own personal interest because they don't come from constitutionalist cultures? Will they vote people because they appeal to their identity (Obama, Yang, AOC, Bernie Sanders, Warren, Harris, Stacey Abrahms, Omar, etc.) or will they try to see past race? Will they value Washington, Jefferson and Lincoln, or will history be rewritten? Will it be 1776 or 1619?
Compare the voting patterns of any ethnicity in America and you'll see there is a distinct trend. Conservatism, republicanism and free market are mostly white and middle class. Other groups don't care about those things; they don't mind doing away with a few ammendments, like we're already seeing.