You missed the point. Cars, knives are tools, same with any blunt object you can imagine. And lots of other pointy things too. And if YOU USE them as such you are charged as such.
But guns are only weapons. They serve no other function but to kill. Thats it. And to kill easily, from a distance, and in many cases to kill multiple times quickly.
BTW, as a rule, carrying a sword, which is also designed to be a weapon, except under certain ceremonies, is generally prohibited.
Basically the only way to use a gun properly, is to either train to, or actually kill something. Thats it. And that is the distinction.