there is a key difference between the two situations.  If the potential blood donor does nothing, the victim will die of blood loss, which is not the same as the donor killing the victim with a knife.  But if the mother does nothing, the healthy child will continue to live.  If she aborts, she is actively killing the child, not just “not helping”.  There is no real alternative to do nothing.  Either she shares her body with the child, or she kills him.  A better analogy is that a homeless person has gotten into your boat but you don’t discover him until the boat is out to sea.  Your choice is to allow him to stay on board until you reach land, or force him overboard – miles from nowhere, where he will die. Even if he doesn’t have the right to be on your boat, does that give you the right to kill him by throwing him off?  And if the person on the boat is a baby that someone else put on board, wouldn’t that be even worse to throw the innocent baby out of the boat?  [Timothy Brahm, Equal Rights Institute; “ Blood Donations and Bodily Rights Arguments”. 
   

        The pro-life viewpoint can be well defended by simple logic and reason.  If you maintain a respectful attitude, are willing to listen, and establish common ground, a productive dialog can be very effective in helping those who are pro-choice to change their minds.