I'm sorry, but this scenario doesn't make any sense at all to me. Why not just punch him? You wouldn't have to kill him, and I'm afraid I don't see how you could anyway, short of drowning him yourself.
Of course just punch him - but that could kill him. If you knock him out cold, he immediately drowns. If you don't hit hard enough to knock him out, he probably still clings for dear life. Let's say that punching him hard enough has a 50/50 chance to kill him. Let's also suppose that you figure that if you manage to get him off you without knocking him out, he has a 1% chance of making it, on his own, to the nearest lifeboat.
Let's also say that you figure you're a strong enough swimmer that, if you get rid of him, you are certain to be able to get to that lifeboat. And that if you let him cling to you, you have about a 60% chance to make it, in which case you also save him.
Do the numbers: you have a better mathematically expected number of survivors if you let the guy cling on. Does that mean you're obligated to let the guy cling on? Not just that it would be the virtuous, heroic thing to do -- that's a given -- but you're
obligated to risk your life?
Your argument is really irrelevant, though. In your scenario, there is an immediate, impending, and thoroughly certain death coming for one or both of you. In the case of pregnancy, there is only a small chance the pregnancy will result in death under normal circumstances.
But the risk to life is only a small part of the problem. Probably the biggest, to a woman who understandably feels that the rape pregnancy is a 9 month long violation, is the sheer invasiveness of it. Defense against threats to your life is not the only valid kind of self-defense. As I said before: If killing in self-defense against the invasiveness of rape is justifiable, then killing in self-defense against the invasiveness of pregnancy is also justifiable.
I don't think [forced kidney "donation"] is comparable at all, for several reasons. The largest reason is that you can live without a kidney - it isn't comfortable, and it sucks, but you can do it.
That would just be ALL THE MORE reason to force people to donate kidneys when someone is in need and when there aren't enough voluntary donors. Is that really the policy you favor?
It's not metaphorical at all. There's no comparison happening. You don't have to sign a release to waive rights. This is absolutely literal. If I have a right to something (a fetusless uterus in this case) but can lose that right by doing X, if I do X I have waived that right. If other words would make you happier, by all means, translate this into something you like better.
So I was wrong about the metaphor: "waive rights" is still the wrong term. Waiving rights means deliberately relinquishing them. By contrast, this is a case of moving into a new situation, up to the limits of your rights, while retaining the same fundamental rights. The appearance of "lost rights" is created by describing those rights in non-fundamental terms.
By your way of talking, I "waive my rights" to swing my fists by walking into a crowded room. But that's not the right way to think of it. I still have the same fundamental right of freedom of movement. I just don't have the right to swing my fists all around me because I have moved myself into a new situation, moving up to the limits of my right.