--> "If there is a kid and a Dad in a canoe and the kid has a contagious illness that has a .02% chance of killing the dad, then the dad isn't allowed to murder the kid to spare him the risk of death", the argument is correct, but only because there is a consented risk. If the Dad didn't want to be at risk for the illness, then he just maintains social distancing from his kid. If he doesn't want to ever be around his kid, then he should set the kid up for adoption.
Parents being around kids with a .02% chance of having a deadly illness consented to that risk, otherwise they would just not have the kid. Unwanted pregnancy is not a consented risk.
Because of this, abortion should be legal until the moment of birth, because there is no time where you get prosecuted by the state for failing to take a risk to your life.
Is consent to sex consent to pregnancy? And what are the implications of this?
You make the point that in your scenario, your Dad can't kill you because he consented to your risk. So let's say that your dad keeps his canoe covered (idk man I don't have a canoe), kind of like using birth control, but you sneak on board anyways (birth control fails). Did he consent to the risk of you even if he covered his canoe?
You say that unwanted pregnancy is not a consented risk. But you can't give consent to something that's a biological process, like pregnancy. If I have sex with someone who has an STD, I can't say that I consented to only having sex and not getting an STD. If I eat cake at every meal, I can't say that I consented to only eating cake and not gaining weight.
And if you took an action which you knew would make somebody dependent on you, and they are now dependent on you, you are responsible for their wellbeing. If you take an action which makes a kid, and you end up becoming a parent, you now have a responsibility to take care of your kid. This should include not killing them.
But what if they pose a risk to your life?
What counts as a threat to life?
I don't necessarily think that a 0.02% risk is arbitrary, but I also agree that we don't have concrete thresholds for what counts as arbitrary. I think it ultimately depends on the moral status of the fetus.
Maternal mortality and SMM consists of many factors. For example, morning sickness has the potential to turn into HG, which is life-threatening to the mother and child. But threat-to-life exceptions don't include morning sickness, they include HG, even though morning sickness has the potential to turn into HG. Let's say that this potential is 0.02%.
There's a pregnant woman who is experiencing morning sickness. We have two options: abort (the violent action) and end morning sickness, or give anti-nausea pills (the non-violent action) which could also end morning sickness. What should we do?
0.02% chance of death may seem arbitrary, but it's far closer to 0 than to 100. Pro-lifers care about the kid and the woman, so if we can use methods which aren't abortion to alleviate morning sickness, we should take that route. Although abortion would be a finite solution, if we are interested in protecting our children, we don't take finite violent action until we are absolutely sure that we cannot do anything else to save their parents.
Let's say that the pregnant woman is diagnosed with HG and her risk to life chance rises to 60%. Also may seem arbitrary, but far closer to 100 than 0. Pro-lifers care about the kid, but we also care about the woman, so abortion is considered.
Doctors take the Hippocratic Oath, which dictates that it is necessary to save both patients, so breaching this when they know based on past recorded experiences, gut feelings, and data that they do not have to kill one patient to save another would be wrong. If we value both mother and child, then we should only target the unborn child when we know with almost 100% certainty based on past medical experiences that we cannot do anything else.
