Well, F_alk, you do bring up an interesting theory. :D
I don’t see a need to threaten shooting someone. That’s not my point. My point is not to threaten them, but simply to make it known that they person holding the gun to your head is not going to come out of the situation in one piece either. If that’s not a deterrent to attack, I don’t know what is. Think of it as “self-defense.”
In your last part, if you’re referring to Iraq, then that’s a different situation. That so-called “unarmed” person is not really unarmed. He’s simply hiding his weapon underneath his jacket. In that case, you can try to “talk” to him (which we did with Saddam) but if he won’t listen, you’ve got to draw the line somewhere, and show him who’s boss.