The date at which a foetus might be viable has nothing to do with a woman’s right to choose.
The thing being that we’ve a Sorites Paradox here.
At one end of the process we’ve entirely separate gametes, each housed in their entirely different host bodies. Usually, but not always, there are two people involved in the process. And at the end of that process we end up with a third, entirely autonomous, different and unique, human being.
The process takes some 22 years in our current culture. From the meeting and fusing of those gametes to the near universally acknowledged full independence of that child when it reaches 21 years of age. Actually, it’s getting a little later as child support notionally stops when the child leaves university these days.
Our problem is that this is a Sorites Paradox. It’s very difficult to insist that the unfertilised egg is a human being deserving of all the protections against, say, being torn limb from limb, that we grant to fully independent human beings. It’s equally very difficult to insist that one 3 days from uni graduation is not eligible for those protections. But where exaclty is that dividing line? That’s what the Paradox itself is: where does a pile of sand become not a pile, where does life become life?
I agree entirely, as I always do on this subject, that I’m an extremist. My position is that life starts where positive action has to be taken to stop it doing so. Thus the egg that needs to be fertilised is not life: contraception is fine. But a fertilised egg left to its own devices in a fallopian tube, which will, if left alone, implant and grow and in that fullness of the 22 years become that independent human being? One that requires positive action to prevent it doing so? That’s life. Meaning that Ru-486 (or whatever) is not OK. That’s an abortifacient.
There are subtleties here: an ectopic pregnancy isn’t ever going to lead to that 21 year old. Thus intervention to stop it killing the mother is just fine (an attitude which even the Catholic Church supports even if you’ve got to ask a few times to get them to agree publicly).
But as I say I’m an extremist on this point, something I know and happily admit. I’m also entirely aware that most of the people I share this society with don’t view it this way. further, that the law ain’t ever gonna be the way I think it ought to be.
However, this still leaves us with the point that this really is a Sorites Paradox type problem. There is no clear and solid dividing line. All we can do, when setting the rules, is go with what most people think is about right. And that’s where viability becomes important. Almost all, almost (sadly only almost) are revolted at the sometimes US (and also Chinese for forced abortions) practice of inducing birth then sucking out the brains of the foetus/child (still Sorities here!) so as to make sure that a live and viable baby is not born. Because almost all agree that that’s sometime past that point at which this new human being gains those protections against being torn limb from limb.
Similarly most are, if not happy, will at least acquiesce, in the idea that a gob of 6 week old meiotic cells is not a human being and can be done away with according to the putative mothers’ wishes.
All of which brings us to what the society around us generally believes is the defining point about which is that tipping point in our paradox. I may not like it that my fellow citizens think this way, you obviously don’t either. But they all do: viability is the defining point. Far from that date of the foetus potentially being viable having nothing to do with a woman’s right to choose our fellows regard that as the defining moment. As and when it can be born and live it’s a human, before that it’s not.