There are plenty of reasons to carry knives in public – you buy one in a shop and you have to carry it home, for instance. Chefs carry their own knives around.
People might have penknives for all sorts of things – fishing, for instance.
There are plenty of entirely legitimate reasons that someone might be carrying a knife in public. We've already gone bonkers to the point of having the sort of bans in place that penalise carrying a fold-up fruit knife.
I bought one in France the other year – an Opinel. Used it on holiday, Brought it home and, the following year, out it in my bag, with my picnic for the journey, to take back.
I got stopped at St Pancras and it was confiscated. Bonkers.
