In the class the question about whether or not to shoot to disable someone came up.
Shooting to disable is NOT shooting to stop. Shooting to stop is generally defined as shooting so as to maximize the chance of a hit and to minimize the time that the attacker remains a threat.
In very practical terms, that usually means shooting at the center of the biggest part of the attacker that is visible. If the attacker is not behind cover that means shooting him in the middle of the torso.
You should never shoot to disable, if "shooting to disable" is defined as: "shooting in such a way as to minimize the chances of seriously inuring/killing the attacker". That can be used as evidence to suggest that you were not justified in using deadly force. The reason that is true is that your mindset is important--your reasonable belief that nothing less than deadly force could resolve the situation is a necessary criteria to establishing the legality of your use of deadly force. If your actions, and especially your statements, make it clear that you didn't think deadly force was really necessary (as evidenced by your attempt to avoid using deadly force by shooting to disable but not seriously injure or kill) then you have severely damaged, if not destroyed, your ability to claim self-defense.
The bottom line is that you should NOT be concerned with the prognosis of the attacker.
If you are concerned about saving his life at the moment you are making the decision to fire, then hold your fire. It's almost certain that if your own survival is not the uppermost priority in your mind then there's not sufficient justification for using deadly force.
If you are concerned about ending his life at the moment you are making the decision to fire (as opposed to stopping his attack as quickly as possible) then you are in danger of overstepping the justification that exists in the law. You shouldn't be acting out of anger or with the idea of punishing or taking revenge, or even with the motivation of upholding the law. Your actions should be driven by the desire to survive.
Furthermore, what many people think of as a "kill shot" may actually hurt your chances of rapid incapacitation. For example, if your desire to kill the assailant results in your targeting his head, that will likely reduce your chances of scoring a solid hit since the head is a small target that is armored by the skull, and that also typically moves around a good bit. Aiming at the center of the torso increases your chances of a hit and getting a hit generally improves your chances of getting a stop over shooting and missing.
The simplest way to keep the proper mindset is to understand that deadly force laws are about
preventing loss of innocent life. They are not provided as a way for citizens to punish criminals, to kill criminals, to take revenge on criminals, to help the police, or to take criminals off the street. They are provided as a last resort to insure that innocent victims have the legal ability to preserve their own life in the face of a violent attack. What happens to the attacker is immaterial in terms of the focus of deadly-force laws. The point of the laws is to preserve the life of the innocent defender.