You fail to mention that nobody in that article died. I think it's a fact that it's a lot harder to commit mass murder with a gun than a knife.
You're correct that this type of mindless violence will exist whether gun control is heavy or lax, but it sure makes it a helluva lot harder for someone to commit these acts if semi-automatics and large-capacity clips are eliminated from the equation. Knives and horse manure can be used for more than killings; guns only serve one purpose.