I will attempt to approach it from both sides:
-- Why are you killing me?
I would want to know what reason is behind your motive for killing me. I am open-minded, to an extent, to which I might actually agree with your decision to kill me, if for none but the greater chances at the human race surviving in a capacity that I can agree with. Of course, getting to that point would require much assumptions, which, during your explanation, would require reasoning with me, compromising on some points, to begin describing a base of opinion to which further explanation would be based on. Continuing from the base, multiple external sources and/or events would be needed to show prior deteriorating effects of my existence, whether locally -- inside of my family or community -- or part of a larger issue that is exponentially affecting the continued survival of the world. Unfortunately, at this point, if should the killer be able to get to this point of the explanation, they would have already been arrested by law enforcement, put to shame with some sort of counter-measures, or have shot themselves already due overwhelmingly incoherent and inconclusive evidence supporting terminating my life.
-- Why I should live?
This explanation would be slightly similar to that above, but the base would be toward more emotional reasons, dealing with family and friends, but expounded on to the point of the global affect of my termination, and the reasons for my living will be immediately understood. For a killer to sufficiently believe my death would be beneficial, they would come to realize that they only thought about certain aspects of a small group of effects, and not the overall picture.
These two scenarios are only possible with the confrontation method of killing. Distance style killings, such as remote bombing or sniper shot, would not allow this type of conversation to exist; the difficult task of explanation is avoided in these situations.
