Defying the Immigration Stereotypes

So, if so many illegally immigrating Mexicans fit an American stereotype of being dissatisfied with Mexico and of being lured by the United States itself, then how is it that "Mexicans emerge as the most personally satisfied public [76%] in the latest Pew Global Attitudes survey"? Perhaps we think a lot of ourselves and not a lot about the real reasons why Mexicans might leave a country with which they are for the most part content for one in which they are consistently exploited, stalked, and reviled.