This is a false equivalence. There is a right to bodily autonomy. An embryo doesn’t have rights as it is not yet a legal person until it is born and cannot be considered as a viable individual with its own rights if it cannot exist separately outside its mother’s body with a realistic chance of survival.
This is completely different to a public policy matter regarding whom the state decides to grant rights to marry, which is entirely a matter for legislature because marriage is about state-conferred legal rights/ property etc via state recognition of a relationship. It is, therefore, for the state to make such choices, not individuals, and they should do so within our legal system based on not restricting personal freedoms more than is required to maintain a stable and functioning society and prevent unnecessary harm. In this case scientific evidence shows that marrying a cousin doesn’t meet this test so should not be permissible. Actively prohibiting an action in which the state has no involvement (what women choose to do with their own bodies) is completely different to the state actively endorsing something through state functions, such as conferring legal marital status. I.e. This is the state’s business and realm of decision-making, whereas what a woman chooses to do with her own body is not. There is, therefore, no possible rational argument as to why marriages between cousins should be permitted by the state per the principles of our law, given the scientific evidence.
The case of whether sex between cousins should be classified as incest is more complex because for the reasons above the state generally stays out of personal decisions on relationships however, this comes with the caveat that when something causes proven harm and the harm prevented by the limitation of it is proven to far outweigh any restriction on personal freedoms, the state will step in. It also has to be enforceable.
As a result, the crime of incest exists in law, because the harm this causes both genetically to descendants and to those who are in these (almost always coerced) “relationships” is so high that the curtailment of personal freedoms is necessary in these circumstances, and beneficial to society as a whole, and the sacrifice of personal freedom involved in prohibiting it is minimal given that pretty much nobody in their right mind with freedom to choose would want to do it anyway - it’s almost always abusive. Given the scientific evidence that the harm caused by procreating with cousins (especially over multiple generations) can easily be as significant as that from doing so with parents/ siblings/ aunts/ uncles, and the evidence of many of these “relationships” being coercive, the case for adding cousins to the list of relatives within the definition of incest is clear. There is no significant curtailment of freedom involved: anybody who wishes to can still have children, or marry whomever they like, they just need to pick a partner from the 3 billion adults on Earth of the opposite sex who aren’t a close relative.
Therefore, the balance of rights in this case is a no brainer. It is also easy to prove, easy to enforce robustly, and will actually reduce levels of personal freedom being curtailed overall because fewer people will be coerced into unwanted relationships and for many women it will mean it’s easier to leave abusive relationships, as well as preventing needless harm to children. A clearer “no-brainer” in terms of the balancing of rights and freedoms in determining law could hardly be imagined than the case for legislating against this, given what we now know about genetics.
This is fundamentally different to whether a woman might have a glass of wine during pregnancy. That is a case where education has worked. Far fewer women drink in pregnancy at all now, and those who do drink very small amounts generally, which have not been proved to cause harm in those quantities. In this case we also know that the few who do drink large amounts causing disabilities for children generally do so in an undetectable way (have you seen hammered pregnant women in public?) and there is nobody to report this if this is happening behind closed doors, so making it illegal would be ineffective because there’d be no way to enforce it on the very people who are causing the harm. Also it would be impossible to enforce because there’s no way to prove in many cases that a woman knew she was pregnant, and in some cases women have alcohol problems so making it illegal would actually cause MORE harm to children because it would encourage women not to seek help during pregnancy if they are suffering from alcoholism when this could prevent further harm to their unborn babies.
We know that the education campaign on this issue has worked for the vast, vast majority of pregnant women. There isn’t a resistance in certain population who are citing that drinking bottles of vodka while pregnant is their absolute right and tradition and that people are being prejudiced by telling them not to do so and claiming that the doctors are making up the evidence that it is bad and that the reason that babies of alcoholic mothers are both with disabilities is because the doctors poisoned them with medicine, is there? Yet these were the views expressed in the documentary that I posted the link to regarding the effects on the children of cousins in Bradford: the parents were in denial and some claimed the doctors were responsible for their children being disabled, and the medicine the doctors had provided was the cause!
Again, the outcomes and overall consequences of legislating need to be considered. In the case of sex with/ marriage to cousins, legislating against this actually strengthens women’s ability to seek help or leave what are often abusive and controlling situations: it’s much easiler to prove someone is your cousin than to prove they raped/ coerced/ abused you etc. Prosecutions would act as a deterrent from people engaging in the behaviour in the first place. The ability of women to leave and get help in refuges/ from police is raised. The practice will be reduced by criminalisation and rates will fall sharply and many children will be saved from being born into miserable and painful, short lives with debilitatating and untreatable conditions.