If you want to know how flimsy we hold women’s humanity, start by looking at the laws governing pregnancy. The 1967 Abortion Act is often claimed to have legalised “abortion on demand”. It didn’t. In practice, the 1967 Act modifies the 1861 Offences Against the Person Act sufficiently to allow most women who seek a termination to obtain one within the law under most circumstances – but to do so, a woman must convince two doctors that continuing the pregnancy would cause “grave permanent injury to [her] physical or mental health”. It’s not enough for her to simply say, “No, I do not want to have this baby”. Ever so subtly, our law starts from the position that the default outcome for all pregnant women should be motherhood: it’s left to each individual to persuade the medical authorities she is an exceptional case who should be allowed to determine the use of her own body.

Perhaps this doesn’t sound so terrible to you. Maybe you consider abortion a grave matter, one of such moral consequence that no woman alone should be able to make it for herself. After all, it is the end of human life – a foetus that would become a baby, then a child and then an adult before dying in its turn – and surely any decision that ends a human life is to be taken seriously. Except, all of us make decisions every day about whether or not to support other human lives with our own flesh, and most of us choose not to. For example: 96 per cent of us choose not to give blood even though we’re eligible to, and 68 per cent of us choose not to join the organ donor register. People die on waiting lists. And this is sad, but it’s also acceptable: no one is entitled to your blood or your organs unless you are generous enough to share them.

But giving away a bagful of gore or a chunk of liver that you’re not using because you’re dead is trivial compared to what is asked of the pregnant woman. For at least nine months, she must dedicate her body to the sustenance of another. She will probably experience weeks of sickness and tiredness. Itchiness, varicose veins, chronic heartburn and piles are among the common unpleasantnesses; diabetes and high blood pressure are rarer and more life-threatening, but still routine. At the end of that, she has to give birth: a natural, wonderful process that kills 8.2 women in the UK per 100,000 livebirths. (And that’s a very reasonable rate, compared with much of the world. Both my own labours involved desperately painful complications – failure to progress, placenta failing to detach – that would probably have killed me in the absence of dedicated medical care. I am lucky, though it’s the kind of luck I don’t care to test again.)

Why, then, do we see blood and organ donation as opt-in – but the donation of the whole bodily system entailed by pregnancy as opt-out, and opt-out only under specific criteria? I think I know why: because pregnancy is the only form of corporeal generosity that is specific to the female body. We recognise males as entire beings with an independent moral nature, and understand that it would be an obscenity to compel any man to give up even part of his body for another’s benefit. We see women as a partial, provisional sort of human with bodies intended as a resource for others to use – and yes, we generally accept that some pregnancies need to be terminated for the good of the woman, but we still see legal abortion as a sad necessity rather than the liberating good it actually is for many women, and we cavil about what is really necessary. We obsess about where to draw the line of foetal viability – 26 weeks? 24? How about 12? – while forgetting that this liminal entity is growing in the belly of a full-term, adult female.

That’s why an act to criminalise sex-selective abortion was passed by 180 votes to one in parliament this week. Not because sex-selective abortion is a widespread problem in the UK (it isn’t), not because legislation is an effective way to arrest it where it is a problem (it isn’t), and not because our parliamentarians are concerned about women being coerced into abortion by controlling families (funding refuges would be infinitely more helpful on that point than making pregnancy compulsory). The act passed its first reading because, in the squeamish centre of their understanding, the MPs believe that no woman should be able to get out of pregnancy unless she has a “good” reason. But once we’ve started judging “good” and “bad” reasons, will anything ever be good enough? Is fear of losing your job a “good” reason? Cutting ties with an ex? Planning to finish your education? How about just not wanting to? Lots of families are desperate for children, why shouldn’t women with unwanted pregnancies have the baby and give it up for adoption?

The answer is that the physical and emotional trauma of having and surrendering a child is more than any woman should have to bear unless she chooses to bear it – denying a woman abortion so others can have children is nothing more than compulsory surrogacy. But if you only really see women as a surrogate sort of human intended for others to exploit, I suppose that could seem reasonable. In an appeal in the Court of Appeal this week it was argued that a child born with foetal alcohol syndrome was the victim of the crime of “maliciously administering poison” under section 23 of the Offences Against the Person Act 1861 – even though a foetus is not considered a person under the law, and even though the compulsive behaviour of a woman with alcoholism can hardly be considered to amount to “malice” towards a foetus. If the judges find for the child in this case, the implication is that anything capable of harming a foetus, from emptying a litter tray to eating brie, becomes potentially criminal when done by a pregnant woman. Women who have miscarriages will become suspects rather than patients – something that happens right now in countries that prosecute women for harms incurred in utero.

Once the state is committed to protecting the unborn from maternal “negligence”, how long before someone uses that precedent to attack the legal basis for abortion as a whole? Not long, I suspect. After all, it enshrines the idea that pregnant women must be caregivers above all else, and ending a pregnancy is the ultimate refusal to provide care. None of this would be an issue if we accepted that women are people, and people do not owe the use of their bodies to anyone. But if we accepted that, we would strike out the 1861 Offences Against the Person Act, and we would remove the requirement of the 1967 Act that two doctors must agree a woman knows her own mind. As far as I know, no politician is trying to make these changes. In fact, most feminists (myself included) have preferred to leave the legislation well alone, hoping that the untidy truce of our statutes will leave just enough cracks for women to live in. That is no longer true. From now on, abortion rights must be fought for from first principles, and the first principle is this: my body, my choice.