Mr. Ekman,
This is an excellent question and one that shows a great deal of sincerity. I greatly appreciate your openness and honesty in asking such a question. It is because of this that I have decided to share my view on this topic with you.
I have seen this subject brought up on this forum before and have viewed the responses. Once again I will in no manner ever suggest to someone how or what one should do in a particular situation I will however develop a foundation of fact so that you can build from it and make the best decision based on the circumstances.
A gun is a gun a knife is a knife they are not the same; yet there are certainly similarities.
First off the situation dictates, and the only thing I agree about the others opinion of, "if you use the weapon use it lethally" is one never knows how many opportunities they will get; thus if you specifically chose to utilize a non-lethal strike and you were wrong then you may not get a chance to recover. On the other hand I do believe that the one advantage of a knife is that it does allow one to strike in a non-lethal manner.
This is a stigma that I have carried with me ever since my L.E. time, which is use only the appropriate amount of force. This means that technically you can temporarily stop a threat with a punch but if you don't follow it up, your opponent could conceivably shake it off and counter.
What I have read here from others is BLACK AND WHITE like some new L.E. recruits I have known, but I will tell you the street is hardly ever BLACK AND WHITE. I have always gone from the heart I have been severe when I felt it was necessary but I didn't stop to check a statute book. In other words to take a life because you know that it was a liability not to, is BULL! That frame of mind does not cut it with my karma. Now if someone else's life is in jeopardy then I might be more apt to be severe because I can't afford a mistake, but for me alone, to kill because I know it's better for me in court, thats not how I work.
So with that in mind know that yes, I sure as hell will use a knife defensively, whether I slash at the back of someone's hand, outside of the arm, leg or even the forehead (which is risky), I might on a given situation. I also feel very confident on my ability to recover if that amount of force is not sufficient and know that I have had to come back with a greater amount of force, more than once. I admit this is risky but when I up the force continuum it is severe and I feel much better truly knowing that it was necessary and not just some clever legal effort to demonstrate in a court of law.
Anatomically as we instruct in our classes one has to know how the opponents are built regardless of whether it is animal or human. Simply put for humans the worst parts are on the inside, the inside of the arms, legs, neck etc.
You must understand that a knife can do severe damage with one blow and a slash to the back of the hand can produce very substantial damage but not necessarily debilitating. Thus you will have to determine if instead of the slash you take that opportunity and kill.
If you have never taken a life than you cannot speak of it and yet still the situation dictates.
In the end you must do what your heart says, you can always act like the others suggest; the words are easy to say, " I WAS IN FEAR FOR MY LIFE" but if this wasnt true can you convey that to a jury. Of course the gallery just said, "I would rather be tried by twelve", (you know the rest), but I am not saying they are wrong, I am only saying who I am. I could certainly go on forever here, but I believe I have made my point, if not, please inquire further as this is a very important question.
I will however add, what advice would I give a friend or loved one who might not be trained as I am, or maybe one who has not experienced what I have? I would have to say the same, however I do my best to see that their weapon is a tool and they use all of their other training and abilities in conjunction with the weapon, in order to be victorious.
I know what happens when all bets are off, killing is easy, its after that that worries me. Why do you think so many combat veterans when they age they search for a bond with GOD. Is it forgiveness they look for even though they were doing, "their Duty"?