The Mexican drug violence is near the U.S. border, not the Belize border. Think about it this way: Some three million people, mostly from the U.S., fly into Cancun every year and party. Do you think they would if it was unsafe?
Those bodies were found on the Guat border close to MX, but drug violence will happen anywhere the drugs and money are. And remember, both are all going north, not south. Only the guns travel from the US south.