I'm inferring from your statement that you believe that the only justified use of deadly force is a situation where someone is themselves at risk of physical harm, is that accurate?

As far as caring for them, I don't think anyone is obliged to care for anyone or anything (free will and all that). I do think that the more people that you choose to place into your own personal out-group of "gofuckthemselves", the more of your own humanity you lose touch with.