Outlawing a tool does not remove it from criminal use. Look at England. They outlawed guns how long ago? and yet they still have people shooting people. But even if you got rid of most of the guns, the argument still holds that bad guys will just find another way of doing what they do. So then you outlaw knives, and now only the bad guys will have them, unless somehow you can eliminate a vast majority from the gen pop so that getting a knife by any means is just going to be difficult. Now the criminals will just use field expedient weapons, such as rock, or sticks, or broken glass, or a jar of gasoline and a match.

And yes, you can outlaw stupidity and legislate common sense, but then we'd only have a one party political system.