The cops react to stupid things done by idiots like this freak.
I don't know if it's true that there wasn't a blade extended. It seems pretty silly to be holding a closed knife in a standoff. And, when the pervert reported himself as a dangerous individual, he also said he might have a gun.
If the cops waited for the pervert to charge someone, there's more chance the cop would miss, or even hit someone else. If the suspect pulled and shot a gun, someone else might have been hurt before the pervert is obliterated. So, obey, or be shot. No need to wait until the suspect actually tries to use the weapon.
I have better things to do than looking for ways to condemn a cop for shooting a menacing and defiant pervert who wanted to die.