Okay, but not selling knives to kids really reduces knife crime? I wonder by how much, if at all. I am having difficulties believing it does.

Fires though, I can definitely believe it does prevent some arson.

> Is there a benefit to society of allowing minors to buy knives?

The default is "no ban". You need an argument the other way around. I think it is a silly question by itself. Is there a benefit to society of allowing people to skydive?