If I wanted to make sure someone was KILLED, I would carry something bigger. I'm not looking to kill anyone; just to stop the attack. Furthermore, most of the attacks are stopped at the sight of the gun. Therefore, all calibers are equal in THAT aspect.
The attack stops three ways: The attacker decides to (usually out of fear), CNS damage, or blood loss to major organs incapacitating the attacker. It doesn't mean that it will kill them, but we are talking about a life and death altercation. There are small, easy to carry guns in calibers that are adequate to meet all three scenarios. I don't see the need for .380 ACP when there are other options.