Your argument is the one with the false equivalency. We are never held responsible for accidents against which we have taken reasonable precautions. Here's a more accurate use of the analogy you are using. taken from this paper of mine
Everyone knows that driving is risky. The chance of getting into an automobile accident when driving is probably greater than the chances of getting pregnant while using properly functioning contraceptives. So if somebody gets into an automobile accident, does that mean that they should be held accountable for that, and thus we should forbid doctors from giving them medical treatment?
Note that if we used this reasoning, it wouldn’t be enough to refuse to pay for the medical treatment. You would have to actually make it illegal for doctors to treat them. After all, they knew they might get into accidents before they drove, and they should be willing to face the consequences. If they don’t want to be in automobile accidents, they shouldn’t drive automobiles. It’s a simple fact of logic. Unless you are willing to make it illegal for people to treat auto accident victims, you are going to have to accept that this inference is unacceptable and that women have a right to get abortions when contraceptives fail. People take risks all the time, and we never claim that they have no right to reverse the bad consequences that might befall from those risks.
You might try to turn this analogy against the argument by pointing out that if someone kills another person in an automobile accident, we do hold them responsible. But that is only when that person has committed an act of gross negligence which caused the accident. We do not believe that the mere act of driving makes one responsible for the accident, even though you could avoid all automobile accidents by never driving. Jarvis Thomson concedes that a woman might be responsible in some sense for a pregnancy if she does not take reasonable precautions, but reasonable precautions do not include abstaining from sex altogether.
