Things aren't the problem. People are the problem.
If you have to use a knife to kill someone, you are going to have to get very close to them to do it. You're going to have to be very aware of what you're doing. With a gun.. not so much.
_At least _ two seriously wounded.
"Guns don't kill people..."
Knives are simply much slower and less efficient for the task, especially against forewarned opponents (e.g. most of the potential victims in many mass-killing situations, and potential defenders), and it's vastly more likely the attacker will be stopped quickly even if he manages to kill a few people.