"inside a city you don't need knives, unless they're stored in your toolbox, for your job - which usually aren't the knives best suited to kill people"
Actual Law Time: You may carry, without a good reason, a folding knife of blade less than three inches with no locking mechanism whatsoever. Anything else, you must have a good reason (or its banned outright if its certain kinds of knife.)
On a practical level, you re much more likely to hurt yourself with the first kind of knife than you are whatever you're hitting. Ain't nobody stabbing with something like that. Having one of those close on your fingers (the most likely result) is nasty.
Now, as to need: I know a reasonable number of disabled people who, for reasons of hand dexterity and other such conditions, find dealing with food and packaging while out and about significantly easier with some kind of sharp object. My work canteen has no sharp knives whatsoever, so actually cutting anything up as part of lunch is a massive chore. just because you can;t think of any good reasons for something like that doesn't mean there aren't any.
Most of the stabbings out there are either big fixed blade knives(which, you really don't need to carry around a city) small locking folders (the law is a little knee-jerk in this regard) and weapons of opportunity (kitchen knives, cleavers, etc, screwdrivers, anything sharp and pointy.) and those last few are something you'll never truly stop.