In my opinion, whether or not a fetus is exactly equivalent to a person, or abortion is exactly equivalent to murder, is somewhat beside the point. The relevant questions are:
(1) To what degree is a fetus’s continued existence worth preserving?
(2) How much priority should be given to letting a pregnant woman choose whether to terminate her pregnancy?
Subsidiary to question (1) are several other questions, such as:
(a) To what degree is a baby’s continued existence worth preserving?
(b) What qualities of a baby make a baby’s continued existence worth preserving?
(b) To what degrees does a fetus differ from a baby with regard to those qualities that make a baby’s continued existence worth preserving?
Subsidiary to question (2) are such questions as:
(a) To what degree is someone entitled to make medical descisions regarding her own body?
(b) Does the level of entitlement depend on whether other people are affected by a decision, and on the way in which others are affected?
© To what degree does a fetus share any qualities of “other people” that make them relevant to this decision?
(d) To what degree and in what way does the level of entitlement in (a) depend on the reason why the procedure is being performed?
(e) How much is the degree to which a woman is “responsible” for her pregnancy relevant, if at all?
(f) What factors determine the degree to which a woman is “responsible” for her pregnancy, if this is relevant?
There’s another issue to consider as well: Regardless of whether the legallity of abortion is “justified” in the above sense, should it be allowed to prevent people from pursuing illegal means of abortion? In particular, illegal abortions could pose a greater risk to the woman. Also, if all abortions were equally illegal, it would remove a lot of the disincentive against those types of abortion that are currently illegal in some jurisdictions.
Another issue is the question of what role, if any, the government should play in the matter. For instance, someone could conceivably believe that all abortion is morally wrong, but that it should nevertheless be legal. To what degree should the government enforce moral behavior? What does constitute a good justification for a law?
Most of these questions strike me as incredibly complex. Sometimes I think that the more complex the issue, the more likely it is to be reduced to a bumper sticker. At any rate, if anyone has any thoughts on any of these questions, I’d like to hear them.