Immigration Questions

Mexican President Felipe Calderon visited President Obama and whined bitterly about the famous Arizona law against illegal immigrants, see this Associated Press article on Yahoo News. His complaint raises several questions.

Why is the United States responsible for taking in Mexico's surplus population? Or for that matter, Latin America's surplus population? Why should an eighth of Mexico's population be in the United States illegally? Shouldn't Mexico be responsible for their own people?

I'm just asking.