EDIT: I'm not advocating that carrying a knife is useless. A knife's day to day usefullness merits carrying one. I'm just arguing against the "unequipped victims" = likely target premise.
You can draw your own conclusions, but the vast majority of mass shootings in America's recent history (last 50 years) have been in "gun-free zones" or "weapon-free zones". The stats aren't even close to being the other way around.