No, it doesn't have to be "mass". The question is, is it really the case that people use knives when guns are not available?

Your hypothesis is that people just use the next available weapon, which sounds logical, but is there any data to support it? Have the eurocrazies actually found a way, in general? Maybe most crazies just go and break furniture and laptops instead of stabbing when no guns are available? Maybe they just punch the person that they are unhappy with?

I mean, Europe is around for long enough time so we should have enough data to come to a definitive answer to the question instead of repeating it every time the subject comes in, right? Do people actually use knives when guns are not available and no significant safety benefit is achieved by the European approach?