I think the more important question is: Should we allow a potential life to be forfeited because it is inconvenient? And if the answer is yes, then why stop in the womb? Maybe we should give every family 6 months after the birth to decide whether or not they made the right choice. After all, a baby is completely unable to take care of itself, so is that where we draw the line? There are certainly situations where abortion is a viable option, but it should definitely be tempered with wisdom and common sense. I certainly believe that any fetus that makes it to the 2nd trimester should be allowed to go to term unless there is a direct threat to the mother, or the baby is not viable.
This is a fallacy of argument in logic--you are using a gross exaggeration of a point to make it seem irresponsible by extending its bounds beyond the point where it was meant to be extended to. I think you know that the line was implied to be drawn at birth (or perhaps at the point when the fetus can feel pain, as it has been in my arguments). The reason for this is it is simply a "potential life", like you said, and not a life, as it is in you infanticide example. As long as you are causing no physical harm you are not creating any outcome different than using a condom or a birth control pill, or not having sex at all.
And, like you said, there are some cases where abortion is simply a viable option, like when both the mother and fetus is at risk (or so I think most people would agree--there's no use in putting both lives, the human and fetus, at risk). Who can decide where the line is drawn. Who is to say, "you can have an abortion, but you cannot." Humans are imperfect, and no person or group of people is truly wise enough to make decisions for everybody--especially not when those decisions are being based on holy doctrines or ideas that not everybody conforms to, as a majority of anti-choice arguments stem from (either underneath the argument or blatantly in it).
Also (and this is simply food for thought, not an argument necessarily for pro-choice) a large percentage of abortions are had by the lower classes, theoretically because the woman cannot afford the to raise a child in some resource (money, time or love--something). If you outlaw the choice in the case of abortions, you're likely to have one of three outcomes.
A) The law does not have a large effect on the illegal behavior, but instead the behavior is happening in an undocumented, unsupervised and unsafe way, leaving nothing but a negative effect (as was the case with prohibition).
B) The law is effective to a capacity, and slightly more fetuses are allowed to be made babies than the number of extra lives put at risk. A
slight gain if you are in the camp that a fetus life is equivalent to a human life. This is probably the least likely of these three "likely" scenarios, and will still eventually have the effect of the third situation...
C) The law is effective to a moderately large capacity, more lower class children are being born. Note that back alley abortions are still going on, and you are adding to the pool of those who are most likely to RECEIVE an abortion, especially a back alley abortion. This is also the group of people who are most likely to have pregnancy at a young age. As you raise the number of people in this category (which, if your law is somewhat successful, will occur at a steadily exponential rate generation to generation), you are also increasing the number of people receiving unsafe, illegal abortions. While your percentage of abortions will have gone down, as time goes by you will actually be RAISING the number of abortions, and doing so in a way that is unsafe for both mother and fetus instead of just the fetus.
A situation in which an abortion law is completely successful is a statistical impossibility and therefor not even worth looking at. The likelyhood of an abortion law being even 90% successful is extraordinarily low, as people who have made the decision to receive an abortion have already made a very difficult decision to which legality probably is hardly an issue. I mean, if laws against marijuana, which is not a hugely driving decision, can hardly keep people from using it, then laws against abortion, which is a much more serious, life changing situation, are not likely to have a near-perfect effect.
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