Looks like people should take care of psychotic loved ones themselves vice calling the police then. As normal people understand how to use weapons that can be lethal like, baseball bats and guns, in less than lethal ways.
Following your logic to its natural end, shouldn't police officers walk up and deliver a head shot after every shooting, just to ensure that they haven't "illegally shot someone"?
A reasonable person might conclude that although a psychotic man with a knife might justify lethal force, the situation by definition does not require it, and that lethal weapons do not require lethal use.
Answer me this. Let's say that one of your family loved ones has a psychotic incident and is wielding a machete at the neighbor kids. If a policeman is driving by and stops, would you want that your psychotic relative be have their legs shot or that the officer shoot them in the head? Lethal force is justified, but is it required. Your assertion that it must be both or neither is not at all logical.
I would expect that officer to shoot to stop the threat, period. I would expect him to shoot at the center mass of my loved one's body in order to stop the threat he/she would be presenting to the kids. Deliberately aiming at someone's limbs (arms or legs) is stupid for multiple reasons. One, limbs are in motion at a greater speed and more angles than the torso, vastly increasing the chance of missing and the shot going wild. Also "winging" them does not necessarily stop the threat. Intentionally wounding someone with a lethal weapon opens up a huge vista for the trial lawyers association creative lawsuit division to sue.
A reasonable person might conclude that although a psychotic man with a knife might justify lethal force, the situation by definition does not require it, and that lethal weapons do not require lethal use.
You need to study up on force theory. If lethal force is justified, it is by definition, necessary. If it is not required, it is by definition, not justified. You can't use a lethal weapon in a non-lethal manner without serious civil and legal ramifications for excessive use of force. That's how it works in real life no matter how silly Hollywood gets with movie plots.