The thing is, I believe in moral complexity. Something can be inherently morally wrong and still very much necessary for survival. There are situations where the only available actions are morally wrong. The victim may very much need to take the rapist's life, but that doesn't change the moral calculus, nor should it.

Have you watched Se7en? Specifically, the "Lust" crime scene. The survivor had to make a choice between both of them being killed, or his killing the woman in a slow and horrifying way. There were no good choices, but the point of the crime, for the killer, was that the most immoral action was carried out by the male victim. The fact that he was essentially under threat of death didn't change the morality of the act, and you can tell that the man was more than aware of that fact.

Ultimately, when you take a life, whatever your reason, they aren't coming back. You've ultimately taken everything from that person. Especially these days, where people are more than willing to take a life, especially in situations where they are the ones in power, the sheer gravity of that act needs to be stressed.