I always laugh my ass off when people say a place is "too dangerous". People are people, and as long as you use your head and are polite, you should be good to go. I've been in so many fucking situations where a smile works wonders.
I guess you can be polite when Jose is stabbing you after swiping your pack, make sure to tell him thank you. Desperate people in desperate areas do desperate things. Is all of Mexico dangerous? Nah its not, but a lot of areas are. But if you look like a victim you will eventually be one.
Take for instant OP, hes young(not discriminating, just with age comes experience). He posted hes looking for people with train experience to ride with in another post. Hes probably never set foot in Mexico or even scoped a yard or knows how to operate in one. Hes going out of his element in more ways than one. Once he jumps off that train and hes across the border hes going to "see if the reports of violence are real and accurate." Where there's smoke there's fire brother bear. If you going looking for violence you'll find it easily.
What do you guys think will happen to a 22 year old gringo? Maybe he'll find some mexican crusties that will give him some good company, its possible... But seriously there's more of a chance of him finding that violence hes looking for than good conversation with the locals. There are some life lessons we all should experience, and some that others should lend helping advice as to avert something bad happening. I just don't want to see his picture on the news, after something bad happened and he lost his life.
Sorry for the wall of text, just be safe in whatever you do brother.