I honestly view this point - that there were prior waves of immigration from various European nations, and before that concurrent waves of forced migration from Africa and elsewhere (though this is left unsaid) - as a bit of a non-sequitur, bordering on bait, largely because it happened over a very long timescale into an essentially empty nation. Suppose I answered in the negative (that I don't think there was anything wrong with it). That wouldn't change anything at all about the current debate. It isn't some kind of gotcha, that if I don't have a problem with British/Italian/Irish/German/French/whoever coming during various migration waves it somehow neuters any particular point about how any immigration regime should, in my view, be structured such that there are clear and defined benefits to the people already living in the country. Enumerated elsewhere in the thread, but the H-1B system in particular is for the benefit of industry (POSIWID etc etc). Not people already here.

It is worth noting, though, that after the peak of immigration in the late 19th century and ending in the 1910s, the United States very intentionally shut off immigration to allow time for assimilation to do its work.

I think the main point that I want to make is that attracting all of the world's smartest people to our country, and staying the world's superpower in technology & science, does have extremely 'clear and defined benefits to the people already living in the country'

The United States achieved its super power status during the most restrictive phase of its immigration history, but now we're getting somewhere. Things like Operation Paperclip are clearly good ideas, and should be replicated for e.g. Russian or Chinese scientists, as but one example.

Yes, one of my ideas that I've had for a couple of years is that the US should impose the following sanction on Russia for invading Ukraine- all Russian scientists & engineers in a narrow range of critical industries (nuclear weapons, armaments, missiles, etc.) and their immediate families are now entitled to a Green Card. It'd only be a few thousand people, so not enough for immigration restrictionists to get upset about- but it'd be absolutely devastating for Russia's technological edge. In some ways it'd be worse than any financial sanction, because your economy can always bounce back later, but once you've lost cutting edge scientists the knowledge loss is probably permanent. I think we should do the same thing for Iranian nuclear scientists too (albeit I understand there might be a bit more political pushback on them)

What is currently happening is the exact opposite.

There is a so-called "Technology Alert List" — a list of critical areas (nuclear, missiles, AI, etc.). If a person has a background in one of these areas, they get an automatic U.S. visa refusal during the interview.

Their visa application gets placed on indefinite hold (the so-called "administrative processing"), which can last for years even if it is eventually resolved.

Why? The U.S. government fears espionage. They worry that someone with expertise in a critical field might immigrate to the U.S., secure a job at a company with access to sensitive, export-controlled technology, and then leak that technology to Russia.

Even without espionage, such individuals could gain valuable experience in critical areas and later emigrate back to Russia — a reverse "brain drain."

Yeah I think there's probably two types of an Operation Paperclip 2.0: the first for adversarial countries (Russia, Iran, perhaps China if you squint hard enough though that one isn't as easy), and the second for something like "geopolitical benefactors" if that phrase makes sense. Basically, using immigration as a tool to leach top scientists and human capital from places like Russia, and as an out for folks in places under direct threat (Ukraine). Immigration policy as a geopolitical tool is probably a much more fraught policy discussion but at least it would be an honest one.

By your logic humans are migrant therefore no borders for all....