Probably something close to the latter:
People came here either for refuge or for improvement, largely for their children. Watching much of the US become mexicanized makes it clear that the improvement part is slipping away for non-mexican citizens. That the government does not seem to care that a huge number of the mexicans creating the changes are NOT citizens and are NOT here legally only adds more despair to both legal immigrants and native born Americans.
If you can see future improvement by returning to the auld sod and future decline by remaining here; getting out of Dodge is a reasonable choice.
PS: If any of the original "I know lots of very well assimilated mexicans", and "this is a bit alarmist" posters are reading this today:
C'mon out to lost angeles, hit the shops downtown, drive ten miles in any direction; a little reality might do you some good.
I am a native Californian and lived in LA for about ten years, moving back to Northern CA in the mid-1980's. When I've gone back to LA for visits, I have been pretty shocked at the changes.
When I was in college at UCLA, I worked at a bank on the corner of Pico & Alvarado. I took the job in that neighborhood only to have some credibility for my then Liberal politics in arguing with my more conservative immigrant father. It was an eye-opener for me when I was told to "go back to college gringa and get out of our neighborhood" and I was chewed out by some customers for my lousy skills in Spanish when many of those who couldn't speak English had been in the US for 20 plus years. This was completely unlike my own immmigrant father who had learned English as soon as he arrived in the US because he knew that he couldn't get a decent job or run a business without that skill. I finally quit that job when we were robbed twice and I was attacked in the parking lot, all within a six month period. That doesn't count the experience of watching a guy pee on our front door after the bank bounced his check, a dead guy under a bus stop who was ignored by his own people for hours until one of us in the bank called the police, or not even being able to walk down the street to get a lunch, alone.
Needless to say, that experience (along with a visit to then-communist Yugoslavia a few years later) made me make a sharp right hand turn, politically.
The bigest difference that I see between LA in the 1970's and today is that now that same attitude of the Pico & Alvarado area has spread across all of LA, when before it used to be confined to a few downtown and East LA neighborhoods that most non-Hispanics avoided.