You think it's OK to OC an AR near the president's event? Why? How about an M-16?
I don't care if it's a flintlock, percussion, revolver, semi-auto, or full auto, if its legal to do so, carry on. The Secret Service has said time and time again that as long as that person is outside of the security zone and its legal to do so, they don't have a problem with it. Why should I?
Remember some state do allow ownership of fully auto weapons. Those weapons are able to be carried legally during a person's day to day business. Now, would I carry an AR or AK at an event as that guy did? No, but as long as its legal and someone has the balls to do it, go for it.