[P_Funk]

Originally Posted by Kazuaki Shimazaki II

That's correct, but take it a little further. If we assume the criminal's life is equal in value to yours, you will actually be unjustified in deciding to guard your own existence.

What is with you guys and your need to qualify the value of a human life? The fact is simply that all human life is equally valuable in the broad definition but to each of us certain lives matter more, those being our own and those we love and care for. The natural instinct to defend a life from extinction plays on these personal values of life but even in self defense where we are willing to end another life to save a preferred one we are doing it in a situation where there isn't an alternative. This doesn't debase the life that was ended in the process on value scale, but it does challenge the character of the man or his decisions. I don't believe in capital punishment so I cannot acknowledge that the actions of a man forfeits his life. As such the spark of existance that breathes in every person is seperate from the character which we might impeach by encarcerating or kiling that person. We can't unjustifiably end another life without just cause, and that cause is only the defense of innocent life.

Now this of course doesn't take into account the irrational urges of the emotional person to seek revenge and to punish someone for their evil deeds but there is a reason this is an irrational response. It is motivated by emotion, an emotion which clouds the rational philosophical human being that is above such uncontrolled svagery. This is why the jury of our peers is 12 strangers, and why they are often sequestered.

Consider this mathematically:
Assume Human Life = 100
Do not self-defend: 100*P, 0<P<1, so 100*P<100
P being probability that criminal will kill you. It can never be 1 in your estimate because you cannot read the criminal's mind.
Self-Defend: 100*P1+100*P2, P1=1, 0<P2<1, so 100*P1+100*P2>100
P1=1 because you've already decided to use deadly force for self-defence. P2 represents the probability that the criminal gets off a counterfire and kills you.
As you can see, if you assume a criminal's life as equal to yours, the harm potential in choosing self-defence will always be higher in principle, thus lethal self-defence is immoral. (For the moment, I've ignored the possibility that you can shoot the other guy and fail to kill him, because the possibility exists for both sides.)
Even if he's actively beating you up or raping you, it still won't be justified, because:
Assume Human Life = 100, so 0<Bodily Harm<100, and Bodily Harm + Killing = 100 because Human Life is only worth 100
Do not self defend= 50+50*P (P being the probability that the criminal will kill you in the end)
Self-defend=50+100+50*P2 (P2 being the probability that the criminal will escalate to a deadly method because you chose to self-defend with lethal force, or even non-lethal force)
I've used only deadly methods, but this can be extended to less deadly methods of self defence. At every level, self-defence will involve the chance of getting both sides hurt, while non-self defence will only lead to yourself being hurt at worst. Thus, the end result may be that any kind of self-defence is immoral.
The only way I see self-defence could be valid is to somehow decrease the value of the criminal's life.
For example, you may calculate:
Do not self defend: 100*0.9=90
Self Defend: 10*1+100*0.1=20
So Self Defend wins.
There is some assumption in the Probabilities, of course, but at least it'd be valid.

Math, yuck. And if you can't find a mathematical solution to justifying self defense then maybe math isn't quite the correct vessel for emparting the intangible emotional value of life that we carry with us.

What if you've already assessed, based on the rapist's size and weight for example, that you cannot "chase him off" or "incapacitate him" with any degree of confidence except with deadly force (your concealed firearm)? Stop evading the scenario.

What if what if what if... you evade the unspecific reality of circumstance and keep demanding that I acknowledge every specific scenario that involves me popping someone. I'm not saying don't kill the guy if you can't help it but I'm challenging the concept that the use of deadly force is demanded on all occasions. Police routinely arrest suspects for crimes such as these without even firing a gun. And yet again I challenge why we're even talking about rape here. Its a totally different scenario anyway, one in which the act of bodily harm is already occurring which significantly alters your demanded discretion.