There is no fundamental difference between the white immigrants of the 1800s (ever watched Scorcese's Gangs of New York?) and the hispanic and asian immigrants that are coming in today.
True.
You live in a country that consists ENTIRELY OF IMMMIGRANTS.
Listen. Seriously. Read what I'm going to type here:
100 years ago everyone was freaking out about the IRISH TAKING OVER.
The Catholics were coming to destroy America.
We're still doing fine.
Indeed, IMHO we've been enriched by this.
Personally, I have no problem at all with Latino immigrants (or any other kind for that matter). I'll go so far as to say that I don't even have a problem with the Spanish language gaining in use and importance in certain states. I don't speak it, but I'll make darn sure that my kids do if Latino immigration continues like it has.

Realistically, though, I don't think that it will continue forever. It will plateau, the older generation that doesn't understand English will die out, and their kids will grow up speaking English just fine. And they'll be Americans, adding their cultural significance and value to our own (BORG!).
I guess I believe that if you merge two cultures, the likeliest outcome is that you end up with the best of both. That's not
always true, but IMHO true more often than it isn't. And I see a lot more to respect and admire about Latino culture than I do to dislike... Oh, looks like Flipside and Battuta already covered that.
you act like there's some kind of American culture worth protecting.
our culture is based on what giant multinational corporations decide they can sell us and that's pretty much it.
It's true that there is a lot of materialism in American culture, but that's not ALL of it. There are plenty of good parts too. If you live in America (not just watch it on TV) and still can't see them, then I feel sorry for you.