Well, I believe in erring on the side of not taking lives until it is conclusively shown one way or another.
So, let's talk about a hypothetical drug that we know prevents implantation, and thus causes the death of the pre-embryo. We'll call it Plan C.
Should a rape victim be allowed to take Plan C? After all, the embryo has no positive right to life*.
It should be taken into consideration that, like unplugging the violinist, taking Plan C is not an act of inaction. Nobody would object to having the pre-embryo removed, frozen, and implanted in another woman. Because the taking of Plan C causes the death of the pre-embryo, it violates his or her negative right to live.
Imagine you are out on a cruise and there is a sleeping man in a life raft drifting towards you. You can either do nothing, in which case the man will dock and be saved. Or you can grease the dock, thus causing his death. Because the man is innocent and greasing the dock is not an act of inaction, doing so would be an act of manslaughter.
*Where the pregnancy has resulted from consensual sex, the embryo does have the positive right to life, because his or her mother has placed the pre-embryo in jeopardy, and, thus, has a responsibility towards him or her to protect the pre-embryo from harm.