Mexico, even though in North America and adjacent to the U.S., is a foreign country and has a different basis of government, politics, economy, manufacturing, environmental control etc. than we do. In my mind, the greatest concern relative to Mexican immigration is that if their numbers become too large, they might vote in a manner not in the best interests of the United States, but to the advantage of Mexico. In certain areas(particularly the Southwest) they would be able to carry elections that relate to their own interests or those that relate to Mexico over and above those of the country as a whole.
I couldn't imagine going to live in Mexico and telling them that they need to teach their public school students in English to accommodate me.
We are not in a position to oppress the Mexicans as a race, and I don't perceive that we would want to. They are a larger minority than we are, and have always to my memory, been given the same full citizenship privileges as whites. That bothered me in my youth, since blacks who had been vested in America so long and were citizens, paid taxes, fought in wars etc were not afforded the same. That was not their doing though.
I never noticed any animosity from the Mexicans toward blacks. They just seemed to want to make some money, and would do any kind of work to do it. I think that is still true to a great extent. However, the truth of the matter is that the Mexican population would come much closer to impacting negatively on blacks than vice verso. (jobs, etc.)
Politically, we are more often on the same side of the fence because of shared socio-economic reasons.