Here we see a phenomenon which was addressed in "The Market For Liberty" and I'm sure elsewhere many times.
Statute law, by its very nature, doesn't work. If a law is written to cover a specific instance, bad-guys (or good lawyers) will find a way around the law. So laws have to be written so broadly that they cannot be "lawyered" around.
The problem becomes that the law is now so general that specific cases where application of the law goes beyond all reason fall into its voracious maw. So lawmakers turn around and try to specify what the law really means, and we are back again into the same old boom-bust cycle and the law libraries grow and grow.
What we have is centuries of accumulated statute law, which cannot be fair, just or rational.
It is far past time to push for repeal of laws, not just more laws.
What happens if the "knife law" is repealed? Nothing. If anyone attacks anyone else with a weapon, be it bic pen or claymore sword, it's still an attack and still fully "against the law".