That's the tool/weapon dichotomy of so many everyday items. At a little league game you'll see a stack of baseball bats and it alarms no one. If a half dozen people are carrying the same objects down the street at 1:00am they're clubs and people panic. Very often I'll be toting my work knife case to or from the car on the way to work; within it are ten blades, most of them in excess of 180mm with one being 300mm or around 12". Few would bat an eye to see a guy wearing a chef coat carrying chef's knives.

The same applies to many other tools. In common law there's no problem with a contractor having a crow bar in his work vehicle, but if you're walking down an alley late at night with a crow bar in your duffle bags you may be in possession of "burglary tools".

The problem with the laws, at least IMO, is that the objects are being treated the same regardless of context.

A knife can make a fearsome weapon, that's true. But it's also a valuable tool, in many cases a life-saving one.