What nobody (Libertarian or otherwise) has talked me out of: Strict pro-life beliefs are inherently religious in cause and structure, and therefore the enforcement of such ideas through use of the law/regulations/police is not only authoritarian, but the function of a militant religious state.
It's easy to say "human life is sacred" and leave it at that, but we also must ask why this is so. A Christian may soundly argue, within her premises, that human life is created by God in His image and is therefore fully sentient, spiritual and valued far above plant or animal life. An atheist may typically argue that yes, human life is more valuable than animal life, because we have evolved into the most sentient, evolved consciousness on Earth. Both sides agree on what makes human beings so special, inasmuch as our brains & souls -- our conscious awareness -- is the expression & substance of that value.
Since human life is valued for its self-awareness, it follows that a "human being" that has no awareness, no power to think or feel, may not be logically valued in the same way that a conscious, sentient person is valued. (When a baby is born without a brain, it dies, and is never considered a fully formed human being). Now a late-trimester fetus can scientifically, logically be shown to possess awareness and sentience. A five-months fetus has likely developed the special traits that make human life so valuable, with a brain, a heart and a consciousness. Even if we're "not sure" if fetuses or even small infants are completely self-aware and sentient human beings, it is absolutely wrong to kill them, just as it's wrong to throw a bomb into a building that "may have" people in it. A developed fetus is absolutely a form of human life & absolutely has natural rights.
But the idea that a first-weeks pregnancy, which at that point consists of a mother carrying a fertilized tissue mass, objectively constitutes a sentient and qualitatively human life, is absurd from a secular point of view. Does the woman at this point have the potential to create a human baby? Yes, she does. But so do any man and woman on a date. Has a self-aware human life yet formed and experienced human consciousness? No, it hasn't. From a secular, scientific, common-sense point of view, using the properties of human life as the standard of what human life is, there is no significant moral difference between two people A) deciding not to screw, B) screwing & using birth control, C) screwing, fertilizing (maybe) and using the morning-after pill, or D) screwing, fertilizing/conceiving, waiting two weeks and aborting the fertilized tissue mass. No new consciousness may be rationally shown to have lived, or died. A potential was always there and is always there every day, but that does not equal a human life any more than an abstention from sex equals an abortion.
But maybe that's wrong, you might say, because what about the Bible/Buddhism/Paganism theories of the soul awakening at conception, of reincarnation & the moment of transference, of your belief as a Christian that the soul in fact is birthed or reconstituted at the moment of fertilization? Well, what about them? These are perfectly valid concepts. Anyone is free to believe any or all or none of them & make personal, moral decisions based on those issues of faith or conviction. But it is not okay to enforce those views on your neighbor or on the public. If we say, "Christianity teaches us that every fertilized egg is a soul" and then go on to make laws that force non-Christians to comply (or Christians who do not choose to believe life begins at conception) with the resulting moral standard, then we are not respecting other faiths and belief systems, and we are enforcing a a religious code on our neighbors. I am sure that most everyone at Liberty Forest would defend one's right in a free society to move into a Hindu neighborhood and sell hamburgers or cooked rattlesnake. To the Hindus present, this would be a horrible crime of killing and eating holy, godlike creatures of worship. Who's to say they're wrong about those animals? That is part of their faith and moral worldview. Yet we would defend our restaurant owner his right to disagree with this religious, unproven, belief -- just as we must defend the liberties of those in Christian-filled communities who are homosexual, or Atheist, or whatever heresy they choose to partake in, if it is not objectively shown to be violent or criminal.
It is worth noting that "life begins at conception" is a fairly moderate version of long-held Western religious beliefs about sex and reproduction. Of course the Catholics are still technically against birth control because a condom does, in fact, prevent new souls from conception and birth. I have had evangelical Constitutionalists on DailyPaul tell me that wanking off is evil because "of all the little tadpoles" that die when you do it. Again, I don't necessarily have a problem with people who believe this, but would clearly demonstrate an authoritarian religious tyranny to make laws based on such beliefs that everyone must follow. Some wiseacre at this point might point out the implications of the government making jacking-off illegal and enforcing it using the surveillance powers of the Patriot Act, and of our entire 14 year old population subsequently going to jail as "pre-abortionists." I encourage you.
I think it is curious that no politicians (and precious few citizens) are able to qualitatively separate early/late term abortions -- objective acts of violence vs. acts merely perceived as violent within certain religious belief -- in this simple way. Dr. Paul has suggested, albeit timidly, legislation along such lines. Everyone else seems to be either hardcore anti-all abortion or hardcore pro-anytime abortion. Given the profound, qualitative differences between early/late term pregnancies & the lives they carry, this would appear to be absurd and myopic.
My leanings though are favorably towards pro-life. 
