The goal in a defensive shooting is to stop the threat. Once the threat is stopped, you stop shooting. Sometimes, and ideally, that happens when you warn the person that broke into your home (because you want to do that) or simply drawing your gun on an attacker outside if your home.
If it doesn't, however, you fire to incapacitate your target. By incapacitate, it means to remove your opponents ability to fight back. In a gunfight, that usually means when they are dead or unconscious. If one surrenders prior to that point, you stop firing, but the basic rule of a gunfight is to shoot until your target is no longer a threat. If your target is on drugs, that will probably mean their death and a lot of bullets from you.
The major differences between defensive ammo, target practice, or hunting ammo, defense ammo is designed to impart as much damage per shot is possible without over-penetrating the target. The most efficient way to do that is with hollow-point bullets. When they enter the body, they mushroom out, causing more damage to the target, but slowing down significantly faster than full metal jacket ammo would.
You don't generally use defense rounds for hunting because you ideally want to damage the meat less, and have time in most cases for perfect shot placement to cripple major organ functionality in one shot. Interestingly enough, most defensive shootings or shootings in war are NOT one-shot kills. The human body is incredibly resilient, and if your attacker surrenders, modern medicine has an excellent chance of saving their life.
Hopefully, this will put you into the mind and logic of one of us American gun nuts