I am horrified to have read all three pages of this thread only to discover that, while many people have gone to a great deal of trouble to ask "what if all 50 women said no," "what if your girlfriend had to get raped?" and so on, nobody bothered to ask "what if the women died from complications at childbirth?"
Not all women can give birth, even when we're talking about the last 50 hypothetically "fertile" women on Earth. "Fertile" just means that a woman ovulates and that her eggs (which are only released approximately every month) successfully make it to a place where they can successfully be fertilized by sperm.
You can argue that, in our hypothetical case, we would know for certain that all of these 50 women would be fertile (as I have just explained), free from any diseases (sexually transmitted or not) that would cause either or both the women and their babies to die within a short period of time, free from any predispositions to mental illness that might cause them to suffer so much from post-partum depression that they might kill themselves and/or their babies.... I could go on for a while. Let me instead direct you to this website:
http://www.noah-health.org/english/p...gproblems.html
Just to expound a little on one thing I wrote above, even a lack of known predispositions to certain diseases (and mental illnesses) could never guarantee that something wouldn't go wrong so that a woman (or both a woman and her baby) wouldn't die.
Now talk to me about how it's more important that you risk my life by traumatizing me psychologically (and possibly physically) - on top of the trauma of being one of the last 50 odd people on Earth - in order to impregnate me with a baby that I don't want to have, whose birth might cause me death and/or permanent physical damage (probably involving pain) and will certainly cause me at least several hours of pain and more psychological damage.
I know I made these risks sound really extreme, but isn't it also extreme to assume that all 50 women would refuse to at least try to have a baby? Isn't it extreme to say that it would be necessary to rape any or all of these women in the case that none of them would be willing to attempt to reproduce or - even worse - in the case that not enough of them volunteered to sustain what the smartest of the remaining 50 odd people says is a viable species? (And what are the odds that the "smartest" person is some kind of biologist or other scientist who would have any kind of helpful knowledge on this subject?)
I'll stop before this becomes a treatise. I hope I've made my point.