I doubt that the death penalty is necessary as self-defense in the US for any reason. In Columbia, it's a different story, where drug dealers can do anything and get away with it. In Iraq, you have an unstable situation (thanks to the US) in which there are big risks in keeping certain people alive. In such cases, killing someone who would like to kill you is simply a matter of self defense.

The problem with the low-expense 45 to the head execution is that it is non-reversible, and innocent people always end up being killed when a non-complex execution method is used. Public opinion becomes the reason for executing people, and the public is motivated by rage over a crime, and the rage is focused on whoever is accused regardless of whether they are fully culpable.