One feature of today's immigration that makes it very different from immigration historically is that we share a long border with the émigrés homeland.  Our shared border with Mexico allows relatively easy travel back and forth (as opposed to the Irish, Italians, Norwegians, Et al).  The immigrants of old had to commit to becoming American citizens because there was no going back for them - only going forward.  
 
With south-of-the-border immigrants, that is not a factor, and this creates two classes of immigrants that did not exist in days of yore. 
 
The legal immigrants come here historically with the intention of melding into the American culture in a generation or two (which Hispanic Americans do in large numbers just as the Irish, Italians and others did in past waves of immigration). 
 
The illegal aliens on the other hand really have no intention of committing to being a part of our American culture.  They are here usually to earn a living for their family that they cannot earn back south-of-the-border.  The money, and probably they themselves, go back to a more familiar and culturally comfortable "homeland" at some point. 
 
 That makes them different than the Irish, Italians, Norwegians, legal Mexicans and others who, while they may have been exploited, were citizens with the promise of better things in subsequent family generations.  

And it is unfair to naturalized American citizens of Mexican decent (or any other origin, for that matter).  In fact the illegal aliens from Mexico now out number their legal counterparts by a widening margin, something never before encountered in the history of our nation. 

This situation with our Mexican Neighbor is a new phenomenon in the history of the United State, and it remains to be seen what the ramifications are.