Let me reiterate. Violence is not the answer for one reason and one reason only. Once it starts and everyone joins, it will be very, very hard to stop.
edit: be
Disclaimer that this is early and I may be wrong, but I read that he had a security detail (which seems rather likely). I doubt an attacker with a knife would have had success.
Guns aren't as generally useful as knives. So it makes little sense to have 1.2 guns per person, or really any private gun possession. The price of mass murders, shooter drills, and firearm accidents aren't worth what marginal benefits guns may bring.