Firstly, in this case, the argument goes that if X does harm voluntarily to Y, X`s obligation to Y is to restore him to the status he had before. This is clearly flawed. If I am a Doctor of Medicine, and I stab you in the stomach, then I provide you with appropriate medical treatment so that you recover fully, can I walk away a free man? No, of course not. I may go to jail or have to pay you damages.
The counter to that would be that the stabbing doctor acted with malice, whereas no woman's sex act can reasonably be called an act of malice toward the unborn-to-maybe-be (nor even an act of negligence, so long as contraception was used). In cases where neither malice nor negligence applies, I think it's reasonable to argue that nothing more than restoration can be required.
Secondly, the argument contends that X has voluntarily committed harm to Y. If X voluntarily got pregnant,
Apparently I wasn't clear; the act in question was the sex---which, as you say, can lead to accidental pregnancy, bring us to ...
if something happens accidentally, does anyone bear responsibility for the accident, in this case, X getting pregnant? Our society is full of examples of people bearing responsibility for accidents that have occurred because of something they did. If I accidentally run you over with my car, with absolutely zero intent of causing you harm, I am still responsible for the act and I will probably have to take measures to see that you are compensated.
But can the required compensation be anything beyond restoring the harmed party's status before the act---which in the case of sex-causing-pregnancy is nonexistence?
Where is the harm? There is none. Creating a life is not doing harm, it is a miracle (or biology, depending on your point of view)! The whole argument is completely illogical. X hasn`t harmed Y, X has given Y life!
My bad; I should have said "endangerment" rather than "harm." The zygote/embryo/fetus has been placed in danger of dying without his mother's bodily resources.
It seems to me personally that all other arguments aside, the key pro-life argument is that it is wrong to take a human life (exceptional circumstances withstanding), which any reasonable person can agree to. Until pro-lifers can provide irrefutable, concrete evidence (is there any?) that what exists at the moment of conception is a human life, there will always be pro-choicers.
Thank you MrLeRoy, I have found your comments about abortion most insightful and useful to me. If I think of anymore rebuttal, I will let you know! :-)