Since the purpose of an object can change rapidly and be hidden easily (example: IEDs), any rules based on the intent of an object are highly impractical. Outlaw guns, and only outlaws will use guns 
people will just use knives, bombs, poison...
people will just use knives, bombs, poison...Why did you strike this sentence through?
« Outlaw guns, and only outlaws will use guns. »
This is just plain truth. By outlawing guns, the State makes peaceful people defenseless against violent people. It is just silly.