I've had more people storm out of the room than I can count - usually with them screaming at the top of their lungs while I maintain a conversational tone.
All you have to say is: "It's OK. Just admit that you think it's all right to murder a child for personal convenience. If that's your viewpoint - fine. Just don't use fancy words to pretend it's not a child and that you're not killing it."
Simply stated: Abortion - The Human Sacrifice To The God Of Convenience.