100% Justified

So you get sent to a call of a "Man with a Knife/Screwdriver." 

The caller says she is being attacked.

The call taker hears the caller telling her attacker, "Put the knife down!"

This is all on the tapes and on the dispatch ticket. You go to the scene, you knock on the door. You're prepared for all Hell to break loose. The door opens, and.....

Gee, the described suspect with a knife, held in what can instantly become an overhead stabbing position or a sideways slashing movement, about what....six feet away?

But Officer - why didn't you go non-lethal, you racist bloodthirsty fiend?

Well....

Gee, looks like a baton - specifically an Asp - on the right margin of the frame. So the Officers were prepared for a non-lethal response....except the offender opened the door, with a knife, within striking distance, and refused to drop said weapon. There isn't a Law in existence that says you have to be stabbed before protecting your life, the life of your partner, or the life of the woman who is recorded saying she was being attacked with a knife. For all they knew, she was wounded or dead inside the apartment.

BANG!

Body cameras can be good things a lot of the time.