Yes, but how many people can you kill in a span of 5 minutes with a knife, as compared to a person using an automatic assault weapon? (rifle, gun, whatever). SO, we're back to how many dead bodies is acceptable? Mag capacity? Right? Because the focus on body count potential as opposed to the behavior is EXACTLY that argument and no sane person thinks that if someone killed 20 kids with a revolver and a shotgun that it would be OK which gets us back to not wanting limits on magazines but the repeal of the second amendment.
Also, it is easier to take a person down (attack the attacker) when you are so in close contact with them. That's why the students brought him down.
With a gun, you don't have to be close to the victim and it is almost impossible to bring them down....