After one of my best friends was brutally murdered I spent a lot of time thinking about this.
I lot of the people that I have taught in the past were seeking to learn martial arts because they had been attacked. Many times, they simply didn't know what to do or what they should do.
It's an important question and one that still has not been attempted clearly by anyone on this thread that I have seen.
A number of people said they would not kill someone unless they had to. A few seem to be sitting in their house, stroking their gun and hoping that someone comes in uninvited. One of the most common rationalizations is that anyone coming in their home poses a threat to them and their family.
So.. free of any rationals...
1. What would you kill for?
2. Could you realistically kill?
3. As a follow up... what are you willing to die for?
I sometimes remind my students, if you are willing to kill you should be willing to die. If you get involved in a violent situation, even with training, even with a gun, you run a risk of being killed.
Something everyone should think about... and few do.