I live in a Mexican neighborhood and folks are always riding on the wrong side of the street (and on the sidewalk). There was an article in Bicycling last year called "the invisible riders" -- all about those who ride for transportation, primarily Latina cultures. If I recall, they highlighted a LA community. They mentioned in the article that it's common to ride facing traffic in Central and South America. Made sense to me and explained the behavior I've seen in my neighborhood.

I've made attempts to explain to riders why it's unsafe, but no one seems to care.