Crowded areas, full of people can make defensive shooting difficult and offensive shooting easy. Most people hunker down and stay low but some panic and run. Throw in the facts that the shooter used gas and wore a vest. You have a situation where hundreds of paniced people are trying to stay out of the line of fire, in a low light situation, some blinded by the gas, along injured or dying victims. You are in a situation that would require an accurate head shot from a low position so your fire would not hit paniced inocents, you are in a situation where training and judgement would be critical; there should be no collateral damage from good intentioned people. Acquiring a clear target would need to be a priority, there may be those present who would be willing to make a physical attack on the shooter. One would need to be in this situation, armed, and ready to make a call. I would agree that if there were several carrying it is likely someone would have a shot, but how many could or would make a proper decision. Most CCW holders are taught that their weapon should be primarily used to protect themselves and their family, when you use a firearm and deadly force to protect the public you may do so at grave cost.