dand, my reference wasn't about baja California but California as a state.
My wife is actually from Mex City so I've spent a lot of time there...the smog is horrendous. That's what happens when your government doesn't control smog regulations...but it's really not much worse than Houston, Dallas, or Los Angeles from my experience.
Most of the trouble spots in Mexico where you'd get in trouble are places like Cancun because the cops can easily rob tourists...and I've been to Cancun on a few occasions and if you gave me the chance, I might like the feeling of messing with the typical tourists down there too.
I've happily walked the streets of San Miguel, Guanajuato, Oaxaca, San Cristobal, Playa Del Carmen, and tons of other places late into the night feeling safer than in most places in the US I've been. It's a matter of place and time I think.
Mexico is a very poor country. Poor countries usually don't have much in the way of environmental law...I've traveled quite a bit and they're kind of like polar opposites.