A) The Ten Commandments forbid murder, not killing. They are found first in Exodus 20, and later repeated in Deuteronomy 5.
B) In chapters 19-21, Deuteronomy draws very clear distinctions between lawful killing, accidental killing, and murder, and very clearly lays out the penalties for each if deemed punishable.
It is my experience that the majority of people who throw the Bible, and specifically the 10 commandments, in your face in discussions about the morality of killing are also people who neither believe in scripture, nor study the book to begin with. They certainly don't live their own lives by its guidance.
Personally, I don't have a problem with people of differing religions from mine who believe differently than I do about killing in self defense, and who support their belief WRT self defense killing with examples drawn from their own religion. That boils down to a theological argument, and what they say may or may not resonate with me. But I do take exception to those who are fundamentally ignorant about my own faith and who attempt to frame their arguments about a given issue around a flawed, incomplete, or absent understanding of my faith.
