After living in San Diego for 20 years, I heard all the horror stories down there, and the majority were just shake-downs for money. So the prudent tourist would have a couple of hundred extra bucks for the local police or other banditos down there. But occasionally you'd hear of someone who ended up in one of their jails which is very bad. So the moral of that story is to take any shit thrown your way and do not harm any of them, even if justified. In any sketchy situation, take the Nike defense and just get out of there. If you have thin skin or insist on muy rights, you could get in trouble down there. IN THE PAST, if you stayed in the touristy areas, and didn't get too far off the beaten path, you were generally considered to be safe. But these days, dunno. The drug cartels essentially run the country right now. I would not venture down there. I don't have hard evidence, other than to say, when they tell you you'll probably be ok, if you stay in the resort, don't look for drugs, etc, is probably a clue to stay the fuck away from there. You could also check the latest travel bulletins from the state dept. By the time they actually say something, you know it's pretty legit. So if there are warnings up about Mexico, I damn-sure wouldn't go. I know this sounds like a bunch of rumor and innuendo, but sometimes there's a reason for all that. I think the threat level down there is equivalent to Iraq or Afghanistan; it's just not PC to say so.
The only exceptions are the ex-pats who retire down there. But they always have a "sponsor" so to speak, usually a spouse who is native and makes everything ok with the locals. So if they insist on going, I would highly encourage them to employ a local guide for any move they make. That will USUALLY keep you out of trouble. Do not wonder around by yourselves. If this sounds a bit paranoid, that's because I'm older and stay away from stupid places, stupid people, and doing stupid things. When I was a bit younger, these things were like magnets to me. So I mean I get it, it's a bit edgy going down there and all, I just don't do that sort of thing anymore.