Based on it's past stance of open access to all manner of weapons--even those that have no place in an open and relatively safe (compared to other countries) society--I always thought the National Rifle Association (NRA) was out of touch with reality and common sense.
However, after NRA president Wayne LaPierre's press conference this morning declaring that "The only thing that stops a bad guy with a gun is a good guy with a gun," I find myself in the unaccustomed position of thinking that, for once, the NRA is right (See: "How To Stop School Shootings").
Simply put, times have changed since I graduated high school back in 1985 (yes, I am dating myself here). As Americans, we had far more access to both full and semi-automatic weapons--with more availability--back when I was in high school. There were no routine school shootings or gratuitous violence in our public schools, except in the most chronically-impoverished and socioeconomically dysfunctional ares of our major cities--and even then, buy today's standards, the violence that did occur was tempered by our relative conservative values as a country (again, relatively speaking). The only variable factor that differs then from now was the availability of money and publicly-assessable resources for mental illness-related services, as well as less dubious diagnoses (such as "Oppositional Defiant Disorder" that children/people can use as an excuse for their behavior and lack of self-control). So the argument that "guns are the problem" does not hold water.
Bottom line, it's that our collective mindsets that have changed. Our social values. Our collective romanticizing of all things related to the "excitement" of living on the edge. And since there is no evidence which indicates that things will get better, its best to adapt to the changing times, and make public schools a less attractive a target for cowards out to make a name for themselves (or who are out to cope with their mental/emotional issues in such a questionable manner).
We have armed guards in banks due to the rising incidence of bank robberies, armed sky marshals on airplanes as a result of 9/11, so why not armed guards in public schools?