It’s almost like, it’s not the weapon that’s the problem, it’s who uses it and for what?
Not that it’s important, but if I kill you with my car, it becomes a deadly weapon. It does not matter what was used to murder Austin Metcalf. He could have been murdered with a shoe, and that shoe would have become a deadly weapon. 
So stop arguing with the idiots about what was used. At the end of the day, it was a knife and a deadly weapon.