Every immigrant group that came to the United States maintained a loyalty to their home country until at least the third generation. Why would we expect Mexican immigrants be any different?
The pattern is extremely typical of large group immigrations. The first generation rarely learns to speak English. The second generation learns the old language first and English when they get to school. The third generation speaks English first and is generally more loyal to their new country.
It is true that when immigrants establish insular conclaves that acculturation takes longer. But even that is part of the history of most immigrants from Western Europe when they first arrived in the US. English was not the only language, there were a lot of communities which spoke German, Italian, and French as their first language.
This post is not a defense of illegal immigration or of our current immigration policy. I just wanted to point out that we display ignorance of our history if we go too far in our anti-Mexican rants.
I think many people base their "anti-Mexican rants" more on what Mexicans do after they come to this country, and not simply on the fact that a large number of Mexicans are here illegally, or that they tend to live in their own race-based enclaves. For me, seeing thousands of Mexicans march through our streets while waving the Mexican flag and demanding amnesty is enough to cause me to develop an anti-Mexican leaning.