In many cases, anything can be a weapon, be it a knife, a gun or a garden-hose, it really seems to be down to the mentality of the people themselves.
I seem to recall that a recent survey found that a knife-wound is every bit as dangerous, if not more so, than a bullet wound. I've always personally felt that the existence of firearms is not so much the problem as the availability of them. You'll always get tragic incidents where an argument leads to a utensil being used as a weapon, but the difference with guns is that they are designed with one specific purpose in mind, and that is to kill things (there is shooting for sport, but it doesn't really change the idea that a gun is to kill stuff).
When I was younger I used to be a keen archer, another device with a single purpose, and I literally just had to walk into a shop, sign a form, and I could buy a bow and a set of arrows that could conceivably lead to someone's death.
My own feeling is that someone who wants to kill will find a way to do so, damage limitation would be better achieved by far more investigation into why someone would want a firearm and the safety of allowing that person to obtain it than by prohibition as a blanket solution.