I've traveled in Mexico for 21 years. There has always been an overstated degree of risk that I have thankfully never experienced. We were warned in San Antonio (1999) that in taking our 13 year old daughter into Mexico we risked her being kidnapped and her organs being harvested. Some of the most startling warnings came from people who were born in Mexico and now lived in the United States.
Like many other things in life there's a huge difference in what we hear versus what we actually experience. Danger is a state of mind more than a set reality. Sure, bad things happen in Mexico. Bad things happen here in the US.
Stories like the Arco Norte robbery should serve to expand our understanding of risks rather than to scare tourists away.