If I were carrying, was 100% sober, and had a clean shot at point blank range, I still would not shoot.
In a crowd like that, once the first shots are fired, the fight or flight response of everyone in the vicinity would kick in, and you would see a veritable stampede of people pushing and pulling against the crowd and not being able to go anywhere. In the split second you drew down on the assailant and lined up your sights, a freaked out tourist would likely bump your arm throwing your aim off (even at point blank range) and your shot may fly into an innocent bystander... That, or people in the crowd could believe that you were the assailant and disarm you/ beat you down.
As for the knife, the same situation goes... Too much risk for unintended casualties.
My personal solution is that I try to stay away from crowded areas. I don't know the mindset of others,so it stands to reason that the less crowded a place is, the less of a chance I have in running into someone bent on causing mayhem. I enjoy the city of New Orleans immensely, but I rarely, if ever, travel on Bourbon unless I'm going to meet friends at Lafitte's, or am going to a nearby restaurant.
ETA: having now gone back and watched the video, it seems like the skinny guy had started to push a path through the crowd for them to escape through before the shooting started. A whole lot of drunken, aloof faces in the crowd. Didn't seem like a whole lot of them were able to register what was going on at that moment. Having some drinks is a good time, but not having your wits about you in that situation is about as dumb as you can get.
This post was edited on 2/10 at 7:01 pm