"Consider if you will that personhood is not a natural fact but a right granted by others."
What I understand is: throughout history any number of populations have been, according to the 'law' of the place & time, viewed as something other than, less than, human. This was and is an abuse, not a negation of intrinsic personhood. This was and is a horror and nuthin' more.
In other words: sometimes the law is an ass (and, when it is, it should be beaten into submission [more directly: overstepping law makers should be curbed or hung]).
The law, as I see it, is meant to serve, to guide, to further. As I say: fundamentally, the law is meant to protect the individual's life, liberty, and property. If law (maker, executor) steps away from this, then break the law, oust or hang the makers & executors.
"For instance before the Russian Revolution, during South African Apartheid, and during slavery in the Carribbean and the American south people a lot of people were not granted personhood. Indeed black slaves were considered inferior to real homo sapiens."
Indeed. It was wrong then, and it's wrong now.
"your oppositions will argue that the pregnant woman's rights are more important than the foetus's rights."
They do this now. You've done this, B. What you haven't explained is 'why' your right trumps fetus-person's. Seems to me: your right to choose doesn't start at conception. You exercise it in your choice of sexual partner, in your choice of contraceptive, in your choice to insist your partner wear a condom, and -- before all other choices -- in your choice to have sex to begin with. If your choices lead you to pregnancy at least have the grace to accept responsibility for your choices, and the consequences of those choices instead of obliterating them.
"Then someone might contend that in special circumstances like if the pregnant woman was about die she should have her death hastened by a Caesarian section to save the foetus."
Seems to me: when the choice is made it's always made in favor of saving the woman. I know of no situation where a woman was forced to give birth at the expense of her own life. I do know of situations where women have risked dying to give birth when they could have aborted and avoided the possibility of meeting the Reaper.
Dicey pregnancies: situations like this do arise, yes, but these circumstances aren't the norm for most abortions. Most American abortions aren't performed to save the woman's life, or to negate the result of rape. No, most abortions are done as a kind of after-the-fact contraception, for convenience (an absolutely awful excuse to rub out a human being).