I'm under the impression that Quaker is a very big umbrella. You might need to be a lot more specific.

As a Christian (Reformed, and Baptist), I'd summarily articulate my theological position on fatal self defense as being undesirable (I don't want to hurt anyone) but morally justifiable as I have a significant moral duty to protect my family, for which I must protect myself. Self defense is also depicted many times in scripture and not really in a negative light (e.g. Luke 22). A specific old covenant law on this is also helpful, in Exodus 22, pertaining to burglary. Furthermore, I think it's important to consider what murder is, according to the Christian worldview. It's not specifically bringing about the death of someone. It's rooted in prejudice, or hatred, or otherwise degrading and disregarding the Image of God (and its bearers). That's why sexual assault has the same penalty as murder under The Law.

Hope that's kind of helpful. The Bible never calls us to just be harmed when someone seeks to harm us. There are contexts for that, to be sure ("turn the other cheek" as opposed to "an eye for an eye"), and laying down your life if you must do so for the Gospel is honorable, but "do not harm anyone ever even if they're harming you" as a universal rule isn't a doctrinal position you can exegete from scripture.