Re: What are you capable of doing?
I'm reading the new Stephen Covey book. He does a good job of explaining stimulus/response in western terms. Basically between stimulus and response you have choice. Some people and circumstances have more choice than others. Things you do to improve yourself expand the gap between stimulus and response and give you more opportunity to choose different options.
Practicing martial arts and developing yourself expands your ability to make choices in situations, even if it is just slightly.
It is never a good thing to be put in the situation to have to choose to kill, but there certainly are circumstances where this is a choice that is presented. I think as martial artist or budoka you have to ask yourself "I am doing everything I can to prepare myself for that time?"
No, we can't train to be prepared for situations since we don't know the variables that will be presented, but I think we can train our bodies and minds to be conditioned (good or bad) to be prepared to deal with death, dying, and killing.
One thing is for certain, you cannot prepare for it by avoiding the subject, or not thinking about it. I think you must look death and killing in the eye, accept it, and know it intimately in order to be prepared to deal with it when the time comes. To each person this will be different.