I thought so.He's trying to kill them? I'm fine with it. assuming there are no other options available to them. Also assuming police officers don't wear stab vests in America and aren't trained to deal with a guy with a knife without killing them.
This is an even more reprehensible position than people are giving you credit for. You're not morally opposed at all to someone being killed in self-defense. You just believe the state should have a monopoly on that force or that only those agents authorized by the state should ever be permitted to employ it. This represents the same kind of paternal elitist attitude that was essential to every police state (and especially more brutal collectivist ones).
There is no such thing as a stab vest, at least none that are all that effective. Slash vests, yes, but they offer limited protection from pointed weapons.