Thus the idea that an armed civilian would be in the right place at the right time, to repell an armed perpetrator, is pure fantasy.  It's a fantasy solution to a fantasy problem.  People seem to forget there was an armed guard at Columbine. 

Law enforcement officers often express dismay at the idea of a heavily-armed populace, because upon arriving on scene, how would they know who the bad guys were? 

I learned from my years of martial arts experience is that the it required time and commitment to learn to defend onself in that manner.  One day self-defense classes, in my opinion, were worse than a waste of time: they taught dangerous ideas and while seeking to empower women and people of smaller stature, created more danger for the students rather than less.

One of the more successful myths developed by the martial arts industry is that size does not matter.  My karate instructor put it as succinctly as possible, as was his style.  "Big people beat up little people."  So while it is true that skill can nullify size differential, in the end tends to be the defining characteristic of any physical struggle.

In the case of guns, I would say the defining characteristic is the element of surprise.  I  recall a "Verbal Judo" class I took from Professor George Thompson in which a law enforcement officer role-played a traffic stop and pulled his pistol.  "I'm not quick but I am early" he said. 

This statement spoke volumes.  Although I have not studied the issue carefully enough to do anything but speculate, it does seem that gun violence does not lend itself easily to being solved by return fire.  Keeping the firearms out of the hands of crazy, violent, and dangerous people seems a better solution, and not one that I think Harris necessarily would disagree with, though he has been soundly thrashed by a number of writers about his stance on guns.