Dexter_Morgan - I always prefer to keep things civil (and thus I will work hard to avoid any sort of ad hominem arguments) because there is no reason for incivility. As to your specific post:
First, on the issue of mentally unstable people, I think that as a society, we should prevent them from killing themselves. Often, the problem is some sort of disorder, and with the right treatment, it can be fixed. As a result, the person no longer wishes to kill him/herself and can function normally in society. If we had let him/her commit suicide, however, then this would obviously not be possible. This, however, is somewhat of a peripheral issue to this debate.
Second, if someone actually needed my kidney (as in specifically my kidney, not generally any available kidney), I would be willing to donate it to them. Now, I will admit if they were in need of a kidney because they had more or less voluntarily destroyed their own (through negligence via heavy drinking or something similar), I might have a few more reservations, but if it was through no fault of their own, I would not really mind.
Third, as far as pregnancy resulting from willful sexual intercourse goes, it is not really a "punishment" so much as the natural consequence of specific actions. Yes, women (and only women) bear children and men don't, but that is just how things are. From a sexual/reproductive point of view, men and women are fundamentally different; I think we all know that. I know that this might not seem "fair" but that is not really relevant. Though I don't support the position, there are a number of men who have argued that they wanted the woman they got pregnant to have an abortion but she did not, and now they are pissed that they have to pay child support (which, in my opinion, is their obligation whether they like it or not).
More to the point, though, is that in my opinion, the right to life (which I specifically mean here to be the right to not be killed by the willful actions of someone else) supercedes all other rights. Thus, the right of the child to live supercedes the right of his/her mother to do what she wants with her own body. Sometimes the rights of different people overlap, but the right to life must be paramount over all others. I would agree that legally, in some societies ("some" since a number do in fact ban abortion), a fetus has less rights than his/her mother. This, however, is a purely legal construct that is subject to change. What societies that allow abortion have done is to more or less state that human life, before it is born, is worth significantly less than human life that has been born. I purposely use the word signficant to denote that it is not just a little less (because in that case abortion would only be legal if the mother was in imminent danger of death if an abortion was not performed) but signficanly less because the convenience of the mother is more important than the life of the child. Now a lot of this comes down to the personhood as distinct from human life argument (because a fetus is clearly human life as I defined it earlier). However, to me is it not only wrong but quite dangerous to argue that personhood and human life are somehow distinct and that this distinction is definable. The reason for this is that, if we agree that there is a definable distinction, then there is nothing to prevent us from defining human life in other states as being "not a person." For instance, is someone in a vegetative state "not a person"? Is someone who is, while not in a vegetative state, severly mentally handicapped "not a person"? Essentially, if personhood can be arbitrarily defined as distinct from human life in any one manner, there is nothing to prevent it from also being defined as distinct in other manners.
Finally, on this specific topic, I do not see how it is reasonable to allow someone to be killed, without their consent, because they might end up having a "bad" or "unwanted" life. Unlike a lot of other things (most other things in fact) killing is quite unreversable and permanent.
As to your poll questions, in the first example the mother is clearly morally/ethically obligated to save the life of her child. As to legally, I do not think we should be legally compelled to do something harmful to ourselves which will prevent someone else from dying from natural causes (which is what is happening in your example I presume). This is quite distinct from the abortion issue because, if nature takes it course, the child will be born alive. It is only by the willful act of the mother that an abortion can occur, but it is the natural result of disease that a child with kidney failure will die.
In your second example, I must first state that I believe IVF to be immoral (we should not play God and create human life in a test tube), so the scenario itself should not really exist. However, within the context of the scenario, I would probably grab the toddler mostly because he is a bit more proximate and noticeable. Again, though, the scenario itself is complicated by the fact that immoral actions have taken place and created a bad situation.