Having politically-minded and religious friends, it comes up a lot. And there's that Women's Caucus column in the CT every week or two, so it gets talked about around the office a lot as well.
The short, simple answer I give about my opinion on abortion is that a functioning brain is a necessary part of being human, so abortions are acceptable until the fetus has a fully developed brain, which (in my vague and limited understanding) would allow abortions until the first or maybe even the second month. I say the brain is important both because of general thought about what it means to be "human," and because of my experiences with my grandfather, Gerard Levesque, who died of Alzheimer's. Which in turn ties into my belief that euthanasia is acceptable for the same reasons.
(Which gets to my belief - and this is going to be one long tangent - that life is, in fact, not sacred. Humanity, in the sense of "being a person" and "being humane," is. A person who is a vegetable, who didn't explicitly say that they'd like to be kept alive on tubes, for whom recovery would be as much of a miracle as raising the dead - let them go. This is an extremely controversial sentiment, but some people are worth less than others. John Wayne Gacy Jr., Tim McVeigh - there may be other reasons not to kill them, for example not to make a martyr out of them, but I don't think it's controversial to say that they deserve to die. I'm against the death penalty. I don't have a problem with it in theory, but I'm against it because in practice it's so fundementally flawed that even if you could fix all the glaring problems in the system today, there's still the fact that executing an innocent person is inexcusable. Some people deserve to die, but in 99 percent of the cases mankind is too fallible to make that decision. So, the point is... I believe that in a life or death decision, whether the organism(s) in question has opposable thumbs and 26 chromosomes is not the most important consideration.)
Yup, a long tangent. But while my short answer about abortion is one thing, the matter is more complicated than that. I read somewhere about how people like to think in discrete quantities - true or false, male or female, a heap of sand or just a pile - but that's not how the world works. A born baby is definitely a human being, an unfertilized egg and sperm together in a test tube is definitely not, but between them you don't have a dualism, you have a continuum. Is it a human being at birth? At viability? At nervous system development, as I say? At cell differentiation? At implantation? At fertilization? Or, hell, as people used to believe - at the act of having sex? If aborting a nine-month-old fetus is murder, then is aborting a one-month-old fetus a crime comparable to a traffic ticket? Is there a difference between a potential life and an actual life? At first glance, you might draw the line at fertilization, but there are still problems with that. Namely, are fertility clinics outlawed? Because they work by fertilizing several eggs and waiting for one to implant. And somewhat absurd concern, but one with even greater scope - does a miscarriage get a funeral?
Drawing the line at fertilization might mean that a woman who has an unusually bad period - a possible miscarriage - after unprotected sex should be investigated for manslaughter. Drawing it at birth or viability might mean that an abortion is perfectly acceptable one day and a heinous murder the next. I'm sorry, but I think the best way to handle this and a whole lot of other problems is to admit that there is a continuum and to leave the choice up to individual conscience.