Living in a "no-firearms" country, I doubt of the usefulness of having open access to guns. I think it creates a placebo effect of security. You feel more secure, but the source of the danger is the gun. The more the gun is near you, the more dangerous it is. Sure, if you control the gun, you are safe when you're behind. But you can make a bad manipulation(shoot yourself in the foot for example), or simply be faced to another gun, controlled by somebody else and be in the most dangerous place you can be, in front of a gun.

Normal citizens are rarely the target of the guns. Shooting somebody is a high-risk situation for your future, and have a high cost associated to it. Sane people, criminals or not, are not going to shoot a gun carelessly. Usually, people who shoot other people are stupid, being paid for it, in a rage moment or clumsy. If you educate your citizens well, you can reduce the amount of stupid and clumsy people. You will probably help them manage their emotions, and reduce the full-rage-on moment. You will have only the paid people to deal with. And you don't pay to kill random people.

Also, most of the killing is usually made by deception or surprise. Why? Because the guy you want to shoot could have a gun! You don't want him to have time to ready his gun and position himself in a position he can defend.

Overall, I really think the gun market is a sugar pill market where you pay thousand of dollars to feel better. The situations where:
-Your life is in danger
-You have the time to ready your gun
-You absolutely need to kill the other guy or you could lose your life
these are pretty rare where humans live generally. So, as a tool, guns are not that useful because their usefulness is only in precise and specific situations that rarely or never happen.

The gun has more value in being a placebo and for defining social status(like cars or clothes can be used to) than being a really useful tool.