Terrorist — we’ll call him Shooter A — walks into a crowded room (say, a nightclub) and starts opening fire.  Immediately, some people fall, stricken by Shooter A.  Others instinctively dive under the tables or behind the bar or run out of the room to the bathrooms.

Brave Shooter B, a patron, reacts quickly.  In half a second, he draws his loaded and concealed pistol, and fires at Shooter A.  He misses but one bullet ricochets and hits a bystander.

As that is going on, brave Shooter C, another patron, is just coming out of the bathroom and hears Shooter A’s gunfire.  She takes her loaded and concealed pistol and runs to the main room, where she sees Shooter B fire with his weapon drawn and people are falling down and/or diving under tables.  She shoots at Shooter B.

Brave Shooter D has dived under the table at the first sound of bullets so it takes him two or three seconds to get his loaded and concealed pistol out from his leg strap, but when he does he see Shooter C and Shooter A and he figures it is more than one person so he starts firing on them both.

Brave Shooter E, the bartender, comes up from behind the bar and see the shooter closest to him shooting at people at so he starts shooting at that shooter but then some other shooter starts shooting at HIM.

Everything I have described happens in a span of 3-4 seconds from the moment of the first shot.  As more “good guys with guns” join in, it becomes unclear who the “good guys” and “bad guys” are.

Oh, did I mention that it is a nightclub where the lights are low and the music is thumping and all the shooters have had a little to drink?

The point: The notion that more guns will prevent mass shootings is just plain dumb, and suggested by people who watch too many movies.  Yes, it might work in certain situations (especially if everybody had advance notice that there was a shooter and a description of what he/she looked like), but in the real world, things are often not that convenient.

Oh, and this…