If that's the case why do such laws exist as foldable knives and switchblades being illegal to carry but sturdy full-length ones are fine, in some countries? Why is banning pistol grips considered having prevented or hindered lethality?
I think bans on types of weapons, and on tools that can be used as weapons tend to be based on public perception of who uses them, and for what purpose. Politicians do not consult masters of knife-based martial arts or designers of fighting knives when drafting legislation about knives. Politicians backing gun restrictions in the US famously tend to be unable to explain the function of features banned by their legislation.
