Multiculturalism and Immigration
There is much in this that I agree with -- to the list of countries cited as evidence that true multiculturalism generally weakens societies, I would add Mexico. (However, it might also be useful to consider Switzerland.) I also agree that the emphasis on trying to keep ethnic groups ethnic, rather than encouraging some degree of "Americanization", is generally harmful.
However, even this is also true to a limited extent. I'm proud to be a Dutch-American, and relish the (admittedly small and few) differences that creates between myself and other Americans. However, while I still wish my mother had taught me Dutch as a child, I'm usually pretty glad I speak English. Perhaps one way to put it as that I think of myself as an American with ancestors who happen to have come from the Netherlands, rather than as someone with ancestors from the Netherlands who happens to live in America.
But in general, the difficulties specifically mentioned in the speech are more deserving of the label 'fear-mongering', not 'prophetic'. Sure, political correctness can become pernicious, but it is on the downswing, not the upswing (though, see the work of David Bernstein, especially You Can't Say That!). Lamm mentions 100 languages; how many of these are really ripping apart our cultural identity? The claim that Spanish-speaking immigrants are harming our identity as Americans isn't ridiculous, but I've never met a Bosnian immigrant who didn't speak at least a bit of English (and I've me enough that this isn't a meaningless claim.) Most immigrants seem to want to be American, and if not the immigrants themselves, then their children.
Economic woes are singularly complex, but it is certainly not illegal immigrants who are causing our economic woes. Illegal immigrants are net contributors to our economy, providing a cheap labor source (which means that goods and services are cheaper), and paying far more in taxes than they get back (since, contrary to the 'received wisdom', they do pay taxes, but they rarely ask for refunds). As far as corporate out-sourcing goes, that's the sort of thing that naturally happens -- for the economy generally considered, it's neither positive or negative. It's a change in the sort of economy we have, which does hurt individual workers (and this is a problem we need to think about), but in the long run, it doesn't hurt the economy as a whole, In general, it seems to me that the concerns presented in this email are more alarmist than true.