Krikorian explicitly rejects the notion that the predominantly Mexican ethnicity of the new immigration is an issue, pointing out that America has always had an elastic definition of “white” (which used to exclude Germans and later Irish) and has steadily expanded it.
The fact that most new immigrants speak Spanish means that many new arrivals can live entirely in Spanish-speaking environments, do business in Spanish, conduct legal affairs in Spanish, and come in no contact with American norms at all. ~Scott McConnell 
Scott’s entire review is worth reading, and I intend to read Krikorian’s book, which seems to deserve the high praise it has been receiving, but these two remarks stood out for me since they seem to contradict one another. If most immigrants are Mexican, Mexicans speak Spanish and the fact that most new immigrants’ assimilation is delayed or halted by the fact that they speak Spanish, the Mexican origins of most of the new immigration would seem to be a major part of the current predicament. One need not believe that Aztlan is about to rise up to recognize that Mexico is unusually aggressive in its cultivation of emigrants through its consular offices, as Krikorian acknowledges, and that its President has continued a bad habit of President Fox by uttering phrases that Mexico is wherever there are Mexicans. Even coming from a country with a less well-established sense of historical grievance in an era where unilateral declarations of independence were not sponsored by major powers, this sort of language would have an irredentist ring to it.
The main argument that our economy no longer assimilates unskilled and uneducated workers in the way that it did a century ago is absolutely vital, and so in this sense large-scale immigration from any other country would represent a major problem. However, if one of the reasons why the new immigration is different is that there is insufficient pressure on new immigrants to assimilate, the proximity to their country of origin and the land connection between their old country and ours represent significant differences from previous waves of immigration that reduce whatever pressure is currently being brought to bear.
Then there is another equally important point:
The negative consequences of high rates of immigration remain whether the new entrants sneak across the border or are relatives by marriage of someone who arrived a dozen years ago.
In much the same way that railing against “foreign oil” is a way to avoid talking about the problem of dependence on oil, railing against illegal immigration only makes it seem as if the important issue is simply the legal, documented status of people entering the country rather than the effects a large influx of people has on wages, social services, demographics and politics. Hence the proposals to legalize those who are already here–if all that matters is legal status, the implication is that mass immigration itself would be desirable if only there were a mechanism to accommodate it.