
For a fascinating explanation of why so many Mexicans and others have come here illegally to work and live, see Where is the Wealth of Nations? from the World Bank. (Note: it's a several meg pdf that will download.)
A Mexican migrant to the US is five times more productive than one who stays home. The report is worth reading, especially the executive summary (is there a logical reason why executives don't have to read as much as the rest of us?) where they explain that it's the Intangible Wealth that explains why some countries get rich and others, despite great resource wealth, stay poor.
For the US, the average American (or illegal immigrant for that matter) has access to over $418,000 in intangible wealth, whereas the average stay-in-Mexico Mexican only has access to $34,000 in intangible wealth. Why wouldn't someone want access to our sort of wealth system?
What makes up Intangible Wealth? Well, it's things like the rule of law, educational systems, infrastructure and I would even include our cafes where so many idea people gather to talk. It's very much our system of freedoms, especially the freedom to trust. Trust is the foundation of freedom, because when you can trust others, you're free to do most anything If you always have to be watching those around you, it's rather difficult to focus on the task. Without the ability to trust, there is no freedom. Without freedom, there is no wealth.
So, has anyone noticed how we're not trusting each other as much as we used to? The terrrorists didn't just attack the buildings, they attacked our freedom to trust.