If a location requires that everyone be unarmed, do you think they've an obligation toI got your point: counterfactuals are hard to figure out. You think that this means the preventative effect of armed citizens might be understated.
I was getting at a related point: if we can infer that someone who's armed in a public place has bad intent, we have more opportunity to prevent whatever he's planning to do than if we give him a free pass until he starts shooting.
Personally, I think more murders would be prevented if *anyone* carrying an AR-15 on a college campus is detained and has his gun taken away than by finding out whether he's planning to do a Charles Whitman impression by waiting to see if he actually does it.
ensure that everyone actually is, & that some protection is offered in case an offender attacks?
The number is hotly disputed (a full order of magnitude), but Gary Kleck has found enuf instances
of guns used in self to point towards their efficacy. Even discounting his findings by a factor of 100,
the self defense instances outnumber the number of deaths due to murder (by gun).
Guns and Self-Defense by Gary Kleck, Ph.D.