The fact that carry usually requires training, and that this may contain a piece of useful information about the lawful use of deadly force in no way contradicts my point or makes yours.
You said that merely carrying at a graduation deserves to be punished with violence. I disagree, and believe that carrying should be a civil right even at educational institutions.
Did you see the picture of the two - the large guy is carrying his long gun in a non-threatening manner. If I had been there, I would have kept an eye on him, but not reacted.
The smaller one is trolling for a response at best, and trying to incite fear at the worst - finger on the trigger guard,ready for action, and the barrel slightly elevated - clearing conveying a threat. And threats sometimes get answered.
http://www.businessinsider.com/michael-bloomberg-wants-to-ban-guns-in-chipotle-2014-5