I hope I never have to be in a situation where I have to take someone else's life. But if somebody I cared about was in danger of losing their own, I wouldn't hesitate for one second.
For example, if I see a person pointing a gun at my best friend or my brother. I'm not going to waste time thinking about what that person's goals are or what their trying to get out of the situation, I'm going to start shooting. Reckless maybe but if a split second decision means the life of a loved one or the life of a individual trying to take someone that is precious to me, then consider that guy checked out.