You have to put it in context.
Each knife handed in is a knife someone on a given day chose to leave home with, in possession of.
Either as self defence or as an act of aggression.

Each knife was handed in by one of these people having a change of heart.
Easy to obtain or not, it is a representation of just how many journies have been started with other intentions.

Even if it doesn't make you feel safer, it should at least paint a clearer picture of what's going on out there.

Should we walk about petrified, heck no, but should be be aware... Yup