Another slimy voice
The Houston Chronicle's "Another Voice" section reprints an article from Mexico's El Universal newspaper entitled "Politics of immigration":
The complicated U.S. electoral climate has caused a proliferation of opportunistic proposals by politicians looking for the support of a sector of the U.S. electorate that is very conservative and even racist. That is why they have proposed measures against Mexican immigrants, as is the case with banning identity cards issued by Mexican consulates... [etc. etc. etc.]
Rather than respond to this drivel directly, let's ask why they would write it. The answer - like many other answers - involves money and power. Mexican citizens working illegally in the U.S. send billions of dollars home each year, and there's that little matter of Mexico's lost territories. From a 1982 editorial in another Mexican newspaper (excerpted here):
The territory lost in the 19th century by...Mexico...seems to be restoring itself through a humble people who go on settling various zones that once were ours on the old maps. Land, under any concept of possession, ends up in the hands of those who deserve it.... [The result of this migration is to return the land] to the jurisdiction of Mexico without the firing of a single shot.