Mexican Immigrants

I have never understood why so many Americans are so irrationaly upset about the Mexican immigration "crisis."
This weekend, I drove down a street and 50 or so Mexican men stood along the edge, waiting for work. These men escaped the horrible conditions that reign in most of Mexico, to try and create a better life for themselves and their families. Can you blame them? America is "the Land of Opportunity," and was created around immigration. I'm not sure if the anti-Mexican-immigration issue is big because I'm in Texas, which borders Mexico, or because they are immigrants. Immigrants have always been looked down on by people who have been here longer. The Irish were looked down upon when groups of them migrated here in the time of the Potatoe Famine. People think they have a right to keep "undesirable" people out of "their" country, but their ancesters got here the same way. It doesn't even go to mention that there is no reason for borders and citizenship except for the government to know where everyone is.
American's should be honored that our country is such a "melting pot" and that people from all over the world come to live here.