Why are large chunks of the American right so freaked out by illegal immigrants? Because they are no longer so freaked out by African-Americans.
And in this regard, the politics of 2010 are more like 1910 than 1970.
Over the last century, American politics has tended to see-saw between panics about immigrants and panics about blacks. A hundred years ago, immigration was the more volatile issue. Anti-black racism was brutal and profound, of course, but African-Americans were a familiar group that constituted a stable share of the population. They were also disenfranchised, and therefore less politically threatening. Immigrants from Southern and Eastern Europe, by contrast, were pouring onto America's shores. And they were becoming politically active: joining labor unions, taking over city governments, influencing presidential elections.