A fetus has no opinion, therefore it cannot determine if it wants to die. Without consent of the fetus, no one has authority to eliminate it. It is pure murder, but like all murder the murderer is also a victim. Adoption and birth control should be available as options. We were all fetuses and have yet to meet someone who has openly said they wish they were aborted.
I'm a Christian and a libertarian, and I also believe that life begins at conception, not at the day of birth. I can see why some libertarians would be pro-choice, but I'm also concerned that the unborn child is alive and also has just as much right to live as the mother would have rights to choose. This is the only topic I know of, that I find difficult to apply libertarian values.
I think that sucking a fetus's brain out or slicing it up violates the Non-Aggression Principle. Just because they can't think or move like a more developed human can does not mean that they are not human, and the fact that they are human means that they should be protected like any born person. If capacity for thought defines humanity, then people in comas or people with brain problems can be exterminated. If "viability" or ability to move determine humanity, then paralyzed or, once again, people in comas can be killed with no moral regrets. In biology, they have a word for when a new organism is created. That word is "fertilization"
I believe today the true problem is that our Government and Society does not doe enough to assist our adoption process. If our system was better kept, better managed, and better paid for it would be able to deal with its issues more properly and make it easier to assist those who do not want or can not take care of a child. The reason that this is a situation of someone that needs a voice that does not have one is for the fact that it is a person and has the ability to become such. In all states if a mother is killed while pregnant (never mind which trimester) it is then considered double-homicide. The reason we see this far different then the "tomato" or the "cow" is because likewise we see human life at a far higher standard then that of other life. Animal rights and pro-vegetarianism aside, it is clear that human life is far different in our understanding and our being. Humans are not killed off for there non-productivity because our ethics call us to defend those. Some would call it hypocritical, but human life can't be put on the same scale as all other life and then assume that everything without a voice must therefore have a voice as humans do. And likewise a human life can not be disregarded when it has the full potential to grow.
As MasterLibertarian said, a fetus has no opinion, for, it has no brain. It is, while unable to think, not its own being. It is simply a group of cells with different D.N.A. Then the parents, little more than a sperm cell and an egg cell. Arguing against abortion is the same as arguing against a condom or arguing against raping every women around you. I'm sure most of the children born these ways would still want to have been born, despite their unusual birth. Before a being has a brain, it is not a being at all. Also, plenty of people commit suicide per year and so saying that some people don't wish they were aborted is untrue.
I would hold that the individuals rights are far more significant than any majority that may wish to restrict someone's freedom to have an abortion.
Medical science has provided us with the timetable of when a fetus becomes an autonomous being, and until that moment, the woman has every right to decide what should be done with her body.
If we do not respect a woman's right to have an abortion under medical science, than we have granted corpses more rights than we've granted women. This is unacceptable, and I would have no part of a society that thinks this way.