[ZenGum]

More seriously, I cannot think of any reason to prefer a knife over a gun, if both are legal.

Guns work from a distance. Knives need to get within arms reach.

Guns make noise which immediately attracts attention, which if you're being attacked, is what you want. Knives are quiet, which is what the bad guy wants.

Knives may be "less lethal", but you don't always want that. You want easily controlled lethality. Guns have options of waving it, warning shot, leg shot, gut shot, three in the chest and one in the head ... With a knife, you'd have to be very very skilled to get that kind of lethality control.

And ultimately, guy with a gun usually beats guy with a knife.

This is just all in my head, though, it sounds to me like Pamela has a lot more thought and experience on this topic.