most of the times they don't argue about killing single cells, but an undisputedly multicellular fetus with human DNA.
the conceived egg cell is already a new member of the given species. why? has it to be of a species? if yes, which one other than human? if no, when this "growing clump of cells" become an organization separate from its host? i don't know other event of a pregnancy which more clearly shows that here is something new which was not there before.
"Can a human be a single cell?" can it be 2? or 3? …
> the conceived egg cell is already a new member of the given species. why? has it to be of a species? if yes, which one other than human?
A cell being of a species does not make it an instance of that species, in the same way that a skin cell is a human cell but is not itself a human.
> "Can a human be a single cell?" can it be 2? or 3? …
If a single cell is not an instance of a human, it follows that there is some point during pregnancy where an instance of a human exists where one did not previously. Mostly the disagreement is about where this line is.
> in the same way that a skin cell is a human cell but is not itself a human.
IMO, there is a substantial difference between a conceived egg and any other cells: an egg turns into a human being over time (provided it's left doing its businnes normally), other kind of cells don't operate this way AFAIK.
> there is some point during pregnancy where an instance of a human exists where one did not previously
completely agree. IMO we can even extend it by omitting the "If a single cell is not an instance of a human" condition: even if we qualify a specific single cell to be a human, there must be a point when it became a human.
yes, miscarriage is a real death of a human. is it killing? yes, it can be a result of an intentional act. can it be caused by neglect? yes, then it's the unintentional taking of a human life.
why we usually threat neglecting the born and unborn differently? because they need different level and kind of care: eg. smoking hurts unborn differently than born. did the mother eat honey which happened to be infected and caused her embryo to die? it was not considered neglect until this honey-effect was discovered.
