The problem is that you have to explain why that rule is valid.
It comes from valuing future world trajectories, rather than just valuing the present. I see a small difference between killing a fetus before delivery and an infant after delivery, and the difference I see is roughly proportional to the amount of time between the two (and the probability that the fetus will survive to become the infant).
These sorts of gradual rules seem to me far more defensible than sharp gradations, because the sharpness in the rule rarely corresponds to a sharpness in reality.
What about a similar gradual rule for varying sentience levels of animal?
A quantitative measure of sentience seems much more reasonable than a binary measure. I’m not a biologist, though, and so don’t have a good sense of how sharp the gradations of sentience in animals are; I would naively expect basically every level of sentience from ‘doesn’t have a central nervous system’ to ‘beyond humans’ to be possible, but don’t know if there are bands that aren’t occupied for various practical reasons.
While sliding scales may more accurately represent reality, sharp gradations are the only way we can come up with a consistent policy. Abortion especially is a case where we need a bright line. The fact that we have two different words (abortion and infanticide) for what amounts to a difference of a couple of hours is very significant. We don’t want to let absolutely everyone use their own discretion in difficult situations.
Most policy arguments are about where to draw the bright line, not about whether we should adopt a sliding scale instead, and I think that’s actually a good idea. Admitting that most moral questions fall under a gray area is more likely to give your opponent ammunition to twist your moral views than it is to make your own judgment more accurate.
It comes from valuing future world trajectories, rather than just valuing the present. I see a small difference between killing a fetus before delivery and an infant after delivery, and the difference I see is roughly proportional to the amount of time between the two (and the probability that the fetus will survive to become the infant).
These sorts of gradual rules seem to me far more defensible than sharp gradations, because the sharpness in the rule rarely corresponds to a sharpness in reality.
What about a similar gradual rule for varying sentience levels of animal?
A quantitative measure of sentience seems much more reasonable than a binary measure. I’m not a biologist, though, and so don’t have a good sense of how sharp the gradations of sentience in animals are; I would naively expect basically every level of sentience from ‘doesn’t have a central nervous system’ to ‘beyond humans’ to be possible, but don’t know if there are bands that aren’t occupied for various practical reasons.
I don’t think anyone is advocating a binary system. No one is supporting voting rights for pigs, for example.
While sliding scales may more accurately represent reality, sharp gradations are the only way we can come up with a consistent policy. Abortion especially is a case where we need a bright line. The fact that we have two different words (abortion and infanticide) for what amounts to a difference of a couple of hours is very significant. We don’t want to let absolutely everyone use their own discretion in difficult situations.
Most policy arguments are about where to draw the bright line, not about whether we should adopt a sliding scale instead, and I think that’s actually a good idea. Admitting that most moral questions fall under a gray area is more likely to give your opponent ammunition to twist your moral views than it is to make your own judgment more accurate.