This comment made me get off my ass and remember my YC login. Your post parses correctly, but what you're saying doesn't really correspond with reality.
> Guns can even fire accidentally, with an accidental discharge on dropping the firearm being a possibility on any gun without a firing pin block (which is practically any long gun, the kind you can buy at Walmart in some states, with no waiting period in some states).
Poppy cock. Modern firearms don't just go off [0]. It is true that many long rifles and shotguns don't have a firing pin block. They have hammer blocks instead (the difference being a firing pin block is activated when the shooter grasps the grip, while a hammer block prevents the hammer of pin from making contact with the cartridge until the trigger is actually pulled). Most firearms incorporate multiple safety systems.
Furthermore, every firearm made in America in the last century has been certified as drop safe. The test is that the gun is dropped from a certain height (I think it's 39 inches) onto a concrete floor, with the hammer back and a round in the chamber - ie the worst case 'I was about to shoot something but butterfingered and now my live firearm is falling to the ground." That was instituted by firearms manufacturers after a spate of bad press when a factory defect meant a batch of Colt 1911's could fire if dropped with a round in the chamber (for those interested, the problem was with the strength of the firing pin spring; after several thousand rounds were fired through the weapon, the tension on the spring would be low enough that it could be over come by inertia). The 1968 Gun Control Act made drop testing mandatory.
> A poorly handled gun may shoot in a totally unpredictable trajectory, and a first time user would be unlikely to consider collateral damage. (Nursery behind the attacker?)
Yes, and an orphanage across the street in case you miss popping your own kid.
Here's the thing - everything you're saying is based on some pretty big assumptions that just aren't true. A study conducted back in 2007 by the Force Science Center where people who had never fired a hand gun before were put through simulated gun fights found that "naive shooters ... are amazingly accurate in making head shots at close range." [1] Point and shoot is something we humans tend to do really really well.
The biggest issue you aren't considering is that the biggest advantage of a gun is that you just have to have it. Power isn't shooting someone accurately - it's bringing a gun to a knife fight. Having a knife means you have to close to the target to engage - having a gun means I can stand back and project power.
[0]There are cases where guns will fire accidentally. These are extraordinarily rare, and are generally due to trying to use an unmaintained firearm in a way it isn't supposed to be.
[1] http://www.forcescience.org/fsnews/66.html
EDIT: formatting edit