A secular argument against abortion

In previous posts, I talked about my views on morality of abortion (here and here). If I understand Jeff McMahon correctly, I take my views as very similar to his view.

I focused on the personhood aspect of fetuses, embryos and zygotes and not on the tricky issues regarding the permissibility of abortion for pregnancies involving rape or pregnancies endangering the life of the woman. My personal view is that a person (with all the rights that comes with that status) comes into existence during the 20-22 week of gestation. Abortion is permissible prior to that time on my view. However, there are those philosophers that have advanced arguments that suggests otherwise.

Don Marquis for example, takes the organismic view which suggests that people are organisms. That is, they come into existence just after conception when a new organism comes into existence (as soon as a zygote does or just after conception). Eric Olson takes the view that people are animals, a view that implies that a person comes into existence at about 2 weeks into gestation (when multicellularity, cellular differentiation and other criteria for animal-hood are satisfied). Michael Tooley says that a person must have certain psychological states such as certain kinds of psychological continuity (see here for a debate between Tooley and Marquis). On Tooley's view, people come into existence only shortly after they attain the ability for language (at about age 1). My view roughly is an temporal intermediary of the extremes of these views and it also corresponds to the time frame of most states' laws on abortion.

I think my view is the best view, the most reasonable and defensible. But is it possible that I am wrong and one of the others right? Sure. It's a tricky issue like all issues still in contention in philosophy. Let's say that I'm 70% sure of my position, 10% sure that either Marquis' or Olson's view is correct (that is, person comes into existence within the first two or three weeks after conception) and 10% sure that Tooley's is and 10% sure that some other time is the correct period for personhood. If I'm 70% sure of my view, that means there is a chance that I am wrong and abortion may be immoral (personhood may come into existence before the 20th week). In that case, terminating a fetus or embryo before that time would be immoral. Let's say that there's a 15% chance of that (10% chance that Olson and Marquis are right and 5% for some time in between my view and theirs). Is it worth making policy decisions based on my view knowing that there's a small but significant chance of legalizing certain forms of murder? Even if the social benefits of protecting a woman's right to choose is significant, we have to bear in mind the possibilities that a person's right to life may be seriously jeopardized. In my view, it's a small chance but a significant chance. It is a possibility of a matter of life and death for people we are talking about.

For all but Marquis's view (since he takes the earliest defensible view), the subjective probability that one's view is wrong and that persons come into existence prior to that point must come into the equation in policy decisions. Such a calculus weighing the possibility of life and death based on the social benefits may be distasteful to many but is they support a woman's right to choose, they must answer why that risk is worth it or explain why we should ignore making the risk calculations. For individual people they must live with the fact that even if they hold some later views such as similar to mine or even Tooley's, they may be wrong and they need to take into consideration in their decision that they could be wrong about the moral status of the fetus or embryo. Even a small probability that personhood has come into existence may be enough to deter some from terminating the fetus.

Alternatively, there may be no fact about the matter between all these views (assuming that epistemicism about personhood is false) and drawing a line in the ground somewhere may be the best thing we can wish for. In that case, the calculus may be avoided if we knew for sure that there is no fact of the matter in such closely contested and roughly equally well supported issues of personhood. In that case, we just have to draw a line somewhere much like the law draws an arbitrary line between adulthood and adolescence at age 18 (claiming that there is no fact of the matter about adulthood also implies that epistemicism about adulthood is false).