My background in economics predisposes to absolutely free immigration, a predisposition that I fully indulge in, but most of economists' arguments in favor of open borders come across to nationalists and traditionalist as somewhat.. autistic. Bryan Caplan was recently in a spat with Occam's Razor over immigration in which the later compared Caplan and economists in general to "cultural Marxists" (the clandestine boogie-men of the social Right); Caplan of course worded his cause in terms of efficiency, supply and demand, and cold and harsh optimality. For most of ethic or cultural nationalists, the problem of immigration is more ethereal and one of values and tradition; immigrants are thought to bring incompatible norms that jeopardize society's stability.
Of course the modern Left shares this fixation with culture: essentially none speak about the practical benefits of immigration, only the supposed benefits of sought-after abstract nouns: diversity, multiculturalism, cultural enrichment etc. If anything one might think that the traditional labor interests of the Left would take a stronger stance against immigration, but the mores often overwhelm material advantages.
Economists may end up sounding like the myopic and non-visionary ones who fail to see the truly important battle formations of the issue, but there is indeed good reason for categorically saying that Hispanic immigration will have cultural effects far below the common expectation.
The popular discussion on the topic is driven by the idea that immigrants come to the United States, set up cute immigrant townships and either share their insightful cultures (if you're on the Left) or commit various crimes (if you're on the Right); this caricature is wholly inaccurate. There are still Chinatowns, as there are Mexican communities, but most immigrants filter somewhat directly into quasi-suburban or working class societies without much fanfare.
We have to speak of the issue of cultural "integration" as if it's some grandiose social project that we must meticulously plan and implement with precise government policy, without noticing it's a natural course of humans left alone. Immigrants don't need to be told to learn English; their children don't need to be told to adopt "our" cultural values.
It's more common to hear the elder immigrants complain about how disconnected their American-born from the Old Culture, how decadent they are and how poor and Anglicized their ethnic language is. The small non-English speaking population of the US is basically nothing more than the sum of the old and very recently arrived.
Immigration into the United States may finally get to the proportions that it graced during the Twenties, but there's little chance that American culture will be changed in more than superficial ways.
The cultural Left and Right will continue to celebrate and decry this change of skin drapery, but for most people the discussion is little more important than the number of angels that can fit on a pin. In reality, politics is trying to over-generalize the Culture Wars to immigration, a place where it doesn't belong in the way people typically understand it.