Hmmm. Interesting question, to be honest. I do believe strongly in self defense. You have every right to defend yourself no matter what, if your life is in danger. They already made the choice for themselves, you just need to answer their choice. As for taking another life to save someone else. That is a yes from me as well, mostly because of my military background. Kind of learn that in training and of course if the RoE's (Rules of Engagement) allow it.
Personally, I have taken a life to protect the lives of my squad when I was overseas, but I can say the first time you do take someone's life. It's not an easy choice, morally, but of course you need to do it without hesitation, or it will just be a huge cluster fuck in the end. The question is very open and can have tons of answers to it, depending on the situation and the morals of the one answering it.
Personally, I have taken a life to protect the lives of my squad when I was overseas, but I can say the first time you do take someone's life. It's not an easy choice, morally, but of course you need to do it without hesitation, or it will just be a huge cluster fuck in the end. The question is very open and can have tons of answers to it, depending on the situation and the morals of the one answering it.