The purpose of a firearm in the hands of a defensive shooter is not to kill an attacker. The purpose of the defensive handgun is to stop an attack and to stop it as soon as is humanly possible. What they seem to not understand is that these small calibers, while perfectly capable of causing death, may cause death hours, sometimes days, after the person has been shot.
And that’s it, right there. In other words, “stopping power” is the sine qua non of defensive shooting.