I've read this thread and am a little confused. Can't you buy a knife (not as nice as Neil's, but every bit as dangerous) at your local Wal-Mart, sporting goods store, hardware store, or just about any store on the planet? If I wanted to stab someone, there's probably a dozen good tools in my very own kitchen. I remember getting steak knives from my gas station with every fill-up. As Neil pointed out, knives are designed with the intention of being used for useful purposes, while guns are designed for the sole purpose of killing.
Someone told me the other day that Business Depot has stopped selling box cutters because of 911. This seems to be just as stupid.