Interesting thoughts . . . My daughter (an Efay with an American outfit) is engaged to a Philly Cop, who often travels with her when she's on duty and he isn't. Unfortunately (?) he's not allowed to take any of his metal stuff with him, but it would certainly be one very well trained, not easily identified, defender in the event of trouble.
I'm six feet tall and he makes me look like a dwarf - with a '9-mil" in his hand he'd certainly have had a chance of disarming terrorists with "box-cutters" (for those who, like me, didn't know - that's American for "Stanley-knives"!)
You'd have to consider that pax might get a bit nervous if they glimpsed a gun under the jacket of a civie-dressed guy, but giving cops "staff passes" might be a very economical, yet effective, way of letting the "bad guys" run the risk of running into someone more heavily armed than they are.
As Pigboat says - El-Al don't get hijacked these days! (Should the ammo be restricted to "low velocity" in the interests of everyone?)