Imagine that one morning you wake up and discover that you have been drugged and moved to a hospital (against your will) and find yourself connected to many various medical machines. Strapped to your back is a man who is currently unconscious. A nurse approaches you and informs you that you were kidnapped by the National Violinist Society but then rescued and brought to the hospital (all during last night) and that the man strapped to your back is a world-famous violinist. The poor violinist has recently come down with some kind of kidney failure that would be fatal unless he could borrow the use of a kidney from a person who matched his particular type. The nurse informs you that your kidney was just the right type, so the crazy violinists from the National Violinist Society connected your kidney to the violinist's kidney while you were knocked out. The nurse says, "Now, we could disconnect you from the violinists, but then he would die. And you will only have to remain this way for 9 months, at which time the violinist will recovery from his kidney ailment and can safely be disconnected. So I really am sorry about your situation, but his right to life trumps your right to not be connected to him. So don't you see that you must remain connected to the violinist, whom you did not choose to be connected to, against your will for the next 9 months".
The abortion-choicer who presents this situation to you is counting on the fact that you will agree with their intuition that the given situation is unjust. They suggest that it would be very good and noble of you if you did choose to remain connected to the violinist to save his life, but that you by no means have to remain connected. You may choose to disconnect if you wish because you do have a right to bodily autonomy. You don't have to offer your body up to another person who could use your body to save their life. If this were true, we would all be obligated to donate every spare drop of blood, plasma, bone marrow, etc. that we can spare to other people who could use it. Thus, the abortion-choicer concludes, the same goes for abortion - you may choose to disconnect if you wish.
I agree that the scenario presented is unjust. I agree that you have a right to disconnect from the violinist if you choose. However, this argument does not justify abortion. It may make you pause for a moment, but you will see that it is not justified. I am 100% confident that pro-lifers can make a very strong counter-argument that dismantles this Argument from Bodily Autonomy. Otherwise I wouldn't have brought it up. To begin addressing why you have a right to disconnect from the violinist but have an obligation to remain connected to the unborn human person we must point out the differences between the violinist situation and a pregnancy situation.
- The neediness of the unborn person is caused by the intentional acts of the person they are connected to. This is the most important difference. Unborn human beings are in a state of neediness (when they need to be physically attached to their mothers to survive) because of the acts of the mother and father. They had sex with the knowledge that it may result in the existence of another human being who would be dependent on them for life - they caused this to happen. So to relate to the violinist example - let's change the circumstances a little to better reflect the circumstances of pregnancy. Let's say that you knowingly took part in an act that could cause the violinist's kidney failure. When we add this line to the story, I believe our intuitions tell us that you DO have an obligation to sustain the violinist - you were the reason he needed your support in the first place.
- The violinist is a complete stranger, the unborn are our own children. In order to claim that the violinist situation is the same as abortion, you must accept that we do not owe our children any more obligation than we owe a complete stranger. Again, let's add to the violinist story to make it more like pregnancy. Let's say that the violinist is actually your son. Now we certainly have at least an increased obligation. Maybe this is not quite enough to convince some people that you must remain connected to your son, but it definitely nudges our conscience in that direction.
- The violinist is connected through unnatural, artificial means while pregnancy is a natural, normal event. The very thing that makes the violinist situation frightening is that you wake up and find yourself in a strange, cold place with tubes and wires connected to you. Its an unnatural connection that we find somewhat repulsive. Pregnancy is a natural and normal thing. It is how we all began and many people would call it beautiful. This is a noteworthy difference.
- The violinist has a pre-existing pathology requiring their connection, unborn human beings are exactly where they are supposed to be. It is one thing to have to cure a violinist of a disease you are completely uninvolved with, but it is somewhat different when the person connected to you is biologically meant be connected to you because they are healthy. Even if a particular unborn person has some kind of genetic disease or abnormality - they are not connected to you because he or she is sick, they are connected because that is what healthy unborn babies do.
- Most abortions do not simply 'disconnect' you from another person, they actively kill another person. Most abortions either burn the fetuses alive or tear him or her limb from limb. Consider this scenario: You come home one day to find a sickly, unconscious man on your living room floor. You do have a right to remove him from your home. However, if the only way you can remove the man from your home is by throwing him off a cliff you may not do it. The same goes with abortions - even if you do have a right to 'disconnect' or 'remove' the unborn human being, if the only way you can do that is by actively killing (burning, dismembering) him or her you may not do it. Now, some few abortions do simply disconnect and wait for the fetus to die by itself - so by this argument you could say that some forms of abortion are okay, while the majority of kinds of abortions are not okay. This seems odd, but at least it is consistent (if you ignore the other 4 differences/points I've made already, that is).