Some pro-legalized abortions take the view that technically speaking the unborn are parasites and that they are fair game for destruction because they are dependent on the mother and consume some of her resources. As weird as that argument is I actually like when they present it. I think that middle grounders will immediately realize what a horribly wrong attempt it is to de-humanize the unborn.
By that line of reasoning, a woman would be totally justified in killing her baby a day before its due date.
That absurdity aside, their analysis fails (at least legally, if not morally). While you are never responsible for keeping someone else alive, you are responsible for doing so if you created the situation in which they are dependent upon you. The classic example is a person who is drowning in the ocean. You, as a boater with a life preserver, are under no obligation to help them out of the water. If, however, you were the one who chucked her overboard, then watched her drown, you can bet that a jury would convict your immoral butt for murder, not for ruining her clothes by getting her wet.
Likewise, you are under no obligation to give a dying person a kidney to save his life, but, if you ripped his kidneys out of his body, you would be charged with murder if he died from those injuries. If the only way to avoid his death is to give him your kidneys, you can bet that your options are to fork over an organ or be charged with murder.
I find it scary that people think of little babies as parasites in the first place!