I have been thinking a fair amount recently about the net benefits of immigration, wondering mostly if perhaps that immigration these days does more harm than good, especially for the countries where people emigrate from, like Mexico. My dad is a pretty good example of emigration being harmful: Austria paid for his entire MD all the way through medical school and internship, and then he left.
But I think that when you look at immigrants from poorer nations, then its a foggier picture. They send back a ton of money to support families. Isn't Mexico's single largest source of 'export' income money send back from the US? This is the case for immigrants all over the world. Just about every NYC cabbie is sending the bulk of their money to their homeland. I have also seen the direct result of money being sent to homelands: in Viet Nam, the richest people were often only rich because they had relatives in the US. In Belize, our hotel owner had lived in Michigan for 8 years, and saved up enough to build a small hotel in his hometown.
But on the other hand, if these people who emigrate could not have emigrated, perhaps they would have put that energy into their own countries. They would probably not have earned as much money overall, but they probably would have contributed to their country in other key ways, like changing the culture to break class barriers, or by organizing people to resist corruption. It seems that if there is an outlet for frustrated people with skills, then the ills of that given society will change slower since there would be less pressure.
This is what my father says drove him from Austria: while the government funded his medical education completely, the society was still very conservative and to be a Doctor, you had to come from the "right" family. He felt he would never have a decent job no matter what he did since he was from a working class family and a rough neighborhood. But had he not had the option of emigrating, I don't think he would have capitulated and just worked the shit jobs in the State mental hospitals. I think he would have made a fair amount of noise, which would have helped change that culture of classism.