Not to make this a political discussion, but part of the problem is the proliferation of guns and this is to be expected when everyone carries a gun. The problem with a gun is that before when people got mad and possibly irrational they might have taken a swing at someone and a black eye might be the result. However when either party now has a gun available, a moment of irrational behavior goes to a place where no one comes back from.
For good or bad, we are a gun culture that has been built on fear and incidents like this should be shocking. Unfortunately, they should be expected. Stuff like this sad incident are going to continue and become routine. Remember you just have to THINK your in danger, and you have the right to shoot first.
Now there are many, many responsible gun owners, probably a vast majority. I don't worry about those people, but as gun ownership expands that small minority expands too.
BTW- while I have my own personal opinion about this issue, I don't post this to question the right or wrong of it. Just to point out that this kind of this kind of incident is now here to stay. To quote a great philosopher, "it is what it is".
