A rape victim suffers from the trauma of the attack long after it is done.
A murder victim does not.
A dead giveaway, I'm sure. But even if the victim's dead, the damage has already been done. I don't think I can with good conscious say that death is less of a damage than lifelong trauma. At least that you can cope with.
The life of the rape victim may be made into a living nightmare with scars physical and mental that never truly heal.
A murder victim's wounds
will never heal.
Rape is a dehumanizing form of torture.
And death is somehow better, how exactly? If you had to make the choice, would you rather be murdered or raped?
Stabbing someone in the leg does not have a high probability of ending the threat. The most certain way to end a threat is with the most debilitating attack (the most debilitating attacks are also the fatal attacks), and you do not relent in your active defense until the aggressor no longer poses a threat.
The point of self-defense is not to beat the aggressor into a bloody pulp and murder him. You use only enough force so you can make a retreat and call for help. What's important is that the force you use does not exceed the aggressor's, for if you do then you're no better than him.
Remember that there are non-lethal ways to debilitate people long enough to make a retreat.
You are going past the extreme to make an absurd strawman: If the attacker is unconscious, he no longer poses a threat. If the attacker is crippled and you can escape, he is no longer a threat. If the attacker is dead, he is no longer a threat. No one except you and Reelya is saying to keep attacking once your attacker no longer poses a threat.
Strawman or not, it still proves the point. The aggressor was unconscious, thus the victim could have easily retreated. Instead, the victim started stabbing for various reasons. Revenge is one possibility. Whatever the reason is, the fact that the victim didn't retreat and instead started stabbing an unconscious aggressor is blatantly unjustifiable. The force used was thusly disproportionate.
And FWIW, I've never said that you should keep attacking if the attacker no longer poses a threat. I don't know where you got that from.