Consequences - It seems there are two groups of issues to look at. The fairness or justice of this situation and the problems that arise because of the imbalance. Most people in America value justice. I find it disturbing that I am a part of this injustice. We have the largest military budget in the world.
Illegal immigration is a growing political issue.
The ecological footprint of the people of Mexico is 6.42 acres per person with only 3.46 acres of ecologically productive land per person. The social problems that arise out of the fairness or justice issue are but child's play when you consider the consequences of overshooting the carrying capacity of the Earth. When the fossil fuel runs out if we don't have methods in place of living sustainably for the level of population we have, literally billions of men, women and children will die. Will this happen in our lifetime, our children's or our grandchildren's. We don't know.