On the rape issue: One of the fundamental tenets of any individual-rights-regarding system concerning the use of retaliatory force is that it is to be used only against those directly responsible for the original initiation of force. The guilty party here is the rapist, not the fetus, and the law might legitimately grant its consent to terminate the rapist (as rape is a most abominable crime), yet not an innocent child, even if the latter's dependence on the mother were a direct outcome of the rape.
Let me present a parallel. Pretend that two mutually unfriendly people are neighbors living in the same apartment building in Britain during Hitler's bombing raids in 1940. A bomb explodes upon the building so as to cause all possible exits to cave in while destroying the wall that separates the neighbors. They are, in effect, forced to share the same living space and work alongside each other in an attempt to tunnel themselves out despite (in this scenario) a mutual dislike.
Does this, then, justify one of the killing the other because of the inconvenience thereby caused, despite the fact that neither one of them had caused it, or would it not instead be justice to demand, upon reaching freedom, that the Nazi air marshal who had commanded the raid to occur be tried as a war criminal? (I know this is an immensely unlikely scenario, but so is rape, and both are possible. And the circumstances here are comparable to those of a pregnancy by rape.)
On the life endangerment issue: No individual is obliged to sacrifice his/her life to save the life of another. Thus, when it can be medically proved that the life of the mother is in fact substantially endangered by a pregnancy (what constitutes "substantial endangerment" is a matter for medical science to define via conclusions drawn from empirical observation), then an abortion can be undertaken as a last resort.
But the only situation in which it is possible to advocate legal abortion and remain loyal to the principle of individual rights, and it is not a typical situation. Rather, it is an emergency, occurrences of which sort are addressed by Ayn Rand in the essay, "The Ethics of Emergencies," in The Virtue of Selfishness.
Rand writes that emergencies are exceptions to the rule, and are not the normal state of human existence, or of ethical human relations. To say that some extreme action may be permissible in an emergency is not to extend that permissibility to the realm of normal human existence as addressed by the fundamentals of ethics.
So, simply because an abortion might be justified as a last resort in some very unusual circumstances, this does not at all justify the general legalization of abortion, especially given the fact that the majority of abortions occur simply because a woman had undertaken indiscriminate sexual relations and does not wish to incur the objective consequences of such acts: namely, pregnancy and the obligation to bring up a child.
I don't expect to see our friends on the left address these issues. They are hard cases and point to the fact that the vast majority of abortions are not hard cases. Most abortions are done because the pregnancy is inconvenient for the woman. That inconvenience takes many forms (for example, the woman is in school or the father of the child isn't her husband, i.e., an affair), but as the post shows, these inconveniences don't justify killing a baby.