The knife part should be illegal. But the handle should stay legal.
People should only use their teeth to gnash and cut things. Teeth aren't as sharp, and they're enclosed so you can't drop them or throw them. Also using teeth would promote communal eating. Groups would share one large piece of meat.
I use kitchen knifes when I cook. If I did not have them, how would I chop food up. And if you're worried about people killing other people with them, well...It's not the knife that kills, but the person wielding the knife. I have heard stories of people who kill with a wad of paper - Should we make paper illegal? No, I think not.
You cannot cook. This is just a ruse question for the gun lovers to have their little wacko argument about instruments of death. It doesn't matter gun nuts. Yes, you can potentially kill with any type object, however, the object's purpose may not have been MADE as an instrument of death and that is all a gun is for. What other use has a gun got?
Oh let's not forget the fork and even the spoon. Have you heard of the spoon killer? We should ban everything and crawl under a rock...
You want to be safe? Stay away from humans. Really it's that simple. A knife cannot kill people. A person wielding knife can kill another person. Humanity is what that needs fixing.
I was taught in Martial Arts that everything is a weapon. When you only have 2 seconds to react you must use what ever item you have at that moment. We did a drill where we had every day items on the floor and the items in are pockets that we always carry. Every one had a number and no one knew the others number that would call out the next attackers number then who was getting attacked. I Feel that Murders are mostly reactions at that moment and not planed. You could make every knife and Gun Illegal and Murders would still happen. The FIRST MUDER in the Bible was COMMITTED WITH A ROCK.