I work with roughly 50% Hispanic coworkers. This is office work so we're not out plowing the fields. They're almost all nice people so I've got no complaints there. But from personal experience some consider themselves Americans of Mexican heritage. Others consider themselves Mexicans who happen to have been born/live/work in the US. Big difference in attitude and perspective.
Most of the newer immigrants I run into, both legal and illegal aren't from Mexico anymore, they're from Central and South America.
The biggest single concern I have with illegal immigration (and I have many) is automobile accidents. This doesn't get enough media attention. 20% of auto fatalities in the US are by people with no license. Second biggest factor after DUI. Yeah some of these are citizens with revoked licenses. Most of them aren't. Many of them don't have accident insurance either.