Knives, guns, rental trucks, it makes no difference. People have been killing other people since the first person thumped another person's gourd with a rock. It ain't gonna end anytime soon. And worrying or whining about what is or isn't a weapon is an exercise in futility(or liberal dogma). Example? OK, here goes nothing: My 1911 spends every night about 1-1/2 ft from my head. It has never once turned itself around to point at me. It's an inanimate object. The CARTRIDGE in the chamber, a hollowpoint .45ACP, is chock full of POTENTIAL energy, but needs to be struck by the firing pin, which must be struck by the hammer, which can't fall until the sear releases, which can't happen until the trigger is pulled, which can't happen unless the thumb safety is disengaged, as well as the grip safety depressed, which requires the gun to be held properly by the operator. And while I have, on occasion been cut by a knife, it was always operator error.
My point is, regardless of whether we are talking about a gun, a knife, a hammer, or a pillow, THEY ALL REQUIRE A CONSCIOUS DECISION BY AN INDIVIDUAL TO BE USED AS A WEAPON, BEFORE THEY BECOME DANGEROUS. In other words, the person holding it is responsible for its use, whether as a tool, or a weapon. In OTHER words, the individual is the weapon, the OBJECT is simply a tool to facilitate the completion of a task(for good or evil) decided upon by that particular individual.