...As far as the "crime deterrent" argument goes, my thought is this: I'm in a gas station check out line. Bad gun walks in with a gun in his pocket to rob the place. He sees the gun on my hip and thinks to himself "Oh, I'll just shoot him first."
I don't think I agree. The guy looking to rob a gas station needs a hundred bucks for a hit of dope. He's not going there with the intent of killing anyone. He's going to try and pick a gas station that looks "easy". If the cops are there having coffee, or if a citizen is there armed, or even if it just looks like there's a lot of people there, or there's a lot of cameras, that makes it look "less easy". If the target store doesn't look "do-able", I believe the bad guy is going to either choose another store or at least wait until things look easier at this store.
Armed robbers, any criminals, aren't simply mindless zombies. They employ human thought processes just like good guys. We may disagree with their choice of lifestyle or method of income, but they still think about their own safety and survival above all else. Just like we do.
Sgt Lumpy - n0eq