I just realized that the noise of the gunshot is responsible for a lot of the death that results from the actual gun. Think about this... the situation is tense. The crazy insane guy has the hostage. The SWAT team is about to bust in, and the negotiator is talking frantically, begging the chief to hold off on full breach, to give him some more time. Then, suddenly, A GUNSHOT! LOUD! OW MY EARS! WHO FIRED? Who was it, the crazy insane guy, or one of the SWAT guys, or was it he hero who is going against orders, trying to save the day? Well, whoeverthehell it was doesn't matter, because now everybody is shooting like lunatics and everybody dies. All because of the noise of one gun going off. Now, what if the gun had gone off, but nobody heard it? It doesn't matter who fired the shot or what happened as a result. Maybe somebody dropped dead, or maybe a window got broken. Neither of those would be very loud... the noise of a body hitting the floor, a medium sized sound of the bullet going through glass. Most likely nobody would notice for a few seconds, and when they did, they would be more confused than anything. That would produce the element of time needed for people to react. To think, and to realize that maybe a gun had gone off. Probably they wouldn't just reflexively hammer down on their triggers and send bullets whizzing all over the place. It's likely that things would turn out with a few less dead bodies if the noise of the gun going off hadn't spooked everybody like cattle.
This can be applied to war situations too. Imagine tanks and machine guns and missiles and all of those things that make loud noises. What if they were silent? Scenarios practically erupt from this idea, in which less people get killed because of the absence of instinctual panic that loud noises create.
I guess my point is this. Loud noises make people nervous.