I believe the poster was pointing to strict concealed laws there. I am not entirely sure, but I am guessing New York, Illinois, and California either do not allow concealed carry firearms or have extremely low percentage of carriers. I assume you are referring to the illegally carried firearms which I am sure the cities have plenty of due to gang activity. I work in a rocky mountain state, and I know that over half of my coworkers are armed most days (and myself included). An event like the Paris attack happening in a city in the rocky mountains would most likely have return fire from the civilians.