Back in 2009, ABC’s 20/20 had a segment where they gave some participants more training than necessary in order to get a concealed-carry permit in many states. … And so they put the participants in a situation where a gunman burst into the room. Watch the whole video (which I can’t to embed here).
Guess how they performed under that stress?
As for the academic side of things, if you want a recap of the studies done about whether more guns in an environment are useful, read this Salon article.