The example from the blog that stuck in my mind as a very good one was the hypothetical "lone loon" in a shoping mall full of legally armed (but not really competent) ordinary people. He starts shooting, all and sundry respond as per their natures and a lot more people end up dead as a consequence.
This type of example is used often by the anti-gun side to "illustrate" their point... that said however... cite to me some examples of these wild gunfights actually occuring. I'm sure an example or two might be found if you look hard, but the truth is that it really doesn't happen often. And in fact, most of these "loon with a gun" sprees tend to take place in locations where the general population is unarmed; Schools, Violence-free workplaces, the streets of D.C., Chicagoland Lane Bryant stores, and other places where the carrying of a weapon is prohibited. You don't hear about these mass killing sprees in places where the victim's are armed very often, I question why that is. (Nah, I really don't.)