The big problem is that lots of people (especially American tourists) have eliminated common sense from their braincase while on vacation.
For example..... if you get into a car that doesn't look like a taxi, it probably isn't. Don't be surprised if that ends badly.
If you see someone that looks like they are going to hurt you, trust your instinct and avoid them. Don't ask them for directions. It will probably end badly.
If someone on the street stops you and offers to sell something to you, they probably aren't looking to move quality merchandise. I bet it ends badly if you buy it.
The guy drinking at the bar isn't a tour guide, and the drop dead gorgeous local girl flirting with you doesn't think you're attractive.
The list is endless, but those are a few. People (especially us Nanny coddled dumb-ass Americans) expect that when on vacation everything is supposed to go our way, and the locals are supposed to cater to our every whim. When it doesn't, and someone gets hurt or killed doing something stupid, it turns into a national incident where the country is dangerous, rather than the traveller maknig an error. Granted there are exceptions to this but then again I have heard of people getting mugged and killed in Fargo ND as well........
Can Mexico be dangerous? Absolutely, but so can Minneapolis or Milwaukee.
Do your homework. Find out where the safe and not so safe areas of town are. Stick with the first, and avoid the latter. Talk to the manager at the hotel/resort you are staying at to see what the local customs are (read where the tourists shouldn't go). They are usually pretty honest on those accounts. Also, as recommended previously, contact the Embassy.
Above all, remember that you are a guest, and don't do anything stupid. Use common sense.
My .02, FWIW, IANAL, and all that.