Some people really need to get over their fears. I suppose it could be dangerous if you go to Mexico City, but the Cancun and Playa areas are thier cash cows, they are going to protect that.
Just because someone told you a story of violence, doesn't mean it's dangerous. I bet you could find the same violence within a 40 mile radius of where you live now.
If you are from Europe I would tell you not to come to Ames because of the gang violence in Chicago.