This is absolutely brilliantly stated. My response to the question, "Would I kill someone who was trying to harm my family?" is quite simply, "I don't know".
The problem with these types of questions is they are fraught with emotion and extremism. The fact of the matter is, that vast majority of us will likely never find ourselves with the need to answer that question anyway. Additionally, the question is framed in a way to make it seem like you just don't care about your family if you wouldn't kill another person. Scriptures are yanked way the heck out of any kind of reasonable context to make it mean that if you wouldn't shoot someone with a gun, you're not "providing" for your family.
I find it troublesome that people can so easily say that they would end another human life. The Truth is, God values us all. He died for us all. And as such, I can't just say with complete confidence that I would end another person's life even if they were hurting me or my family.
There is no easy answer to this question for me. If someone were hurting my wife or my kids I would certainly do what I could to stop them, and in the heat of the moment I might just kill to protect them. But I could not pretend like it was my God-given right to do so. I would agree with RDKirk's statement and call it, "A whole sorry, sad, unholy, unrighteous mess in a fallen world."