My husband and I moved from CA to Mexico nearly 15 years ago. We lived in SMA for three years and moved to Ajijic in 2008. We have only been back to the U.S. once: four days for a family funeral. Cross my fingers, but we've had no crime problems and live in a mixed neighborhood downtown. People are friendly and helpful. We became involved in a local professional and charitable organization and have been well content with life. A minor thing, but our income goes much farther here than it would have in CA, so we've been able to afford a few "luxuries" as well as covering the necessities of an expat life. In short...we're here for the long haul and happy.
I'm well aware of the trouble that exists in various places in Mexico and do my best to avoid situations that could be dangerous. However, I lived in the big cities in CA and there is plenty of trouble there, too. In general, one can focus on the negatives...anywhere. Who needs that?