[sexypanda]

Given the new number 1, I don't think anyone can bring up a justifiable defense, but given your caveat of "belief" you are bring in a subjective standard. You then have to put yourself in the person's shoes to see if the belief was reasonable. You have to understand the peron's background and indivudual circumstances. But what if the person was racist and percieved every black person as a threat to him. He then is subjectively justified in killing any black person, but then we have to bring in some sort of objective reasonablness in ("social norm"). I don't think morality is truly only subjective or objective, but I think it can be defined as a counterplay between both standards. If you strictly believe in just an objective standard though, you'll end up coming up with the "wrong" decision in some circumstances.