Well firstly, the gun lovers gave a child an uzi, which he shot, and the kick caused it to recoil back and shoot him in the head. Killing him stone dead. There is a news report on it: http://www.childinjurylawyerblog.com/2008/10/boy_accidentally_shoots_himsel.html
A damn good reading why you don't want guns around, not to mention accidents involving kids and guns in the home.
"Why do you NEED a reason to own a gun"
For the same reason I don't buy ladies underwear. I don't have a requirement for it. It's what police are for.
"and why should they be prohibited from the general population? "
I'll answer that with a direct quote from yourself:
"Of course guns are designed to kill"
Before you start arguing rubbish like "a car can kill in the wrong hands", a car (or any other object you may choose) is not designed to kill. It is designed to transport people (again, or whatever job it is for). A gun is quite simply there to kill. And so by allowing them in the general populous you are giving people a way of killing each other and only that.
Also, as I said before, there are some things I accept you want a gun for. Like you said, sport shooting and hunting etc. But to want to carry a gun down the street clearly shows you are willing to use it on someone, to kill someone. (I suppose it could just be a gonad enhancer?)