I'm going to butt in and say that the pro-choice brigade are kind of dumb asses for concentrating on how developed the thing they destroy is. In my opinion, once the egg has been fertilized, to an extent the eventual human being has already been chosen. Destroying some fetus that isn't developed can't be compared to destroying something that would never otherwise become a human being. You're only doing it because it would otherwise become a human being. If time travel was possible and you could go back and make who ever mocks this post not exist by making their parents never meet, that would be murder.
People hate the 'potential life' argument, because masturbation effectively destroys potential lives. I'd argue that it's like comparing spilling flour on the floor to throwing a half baked cake out of the window.