I sometimes wonder if our tighter border security is preventing the frequent back-and-forth movement that characterized Mexican migration for most of the 20th century. That would create some negative impacts, as people couldn't leave the US when jobs were few, and couldn't easily re-enter when they were plentiful. This additional money would have strengthened the Mexican economy, and probably contributed to social stability.
Now, shit's a mess. Paramilitary gangs. Paramilitary border patrol.