The internal logic is consistent with their stance on abortion, if you think about it. The pro-choice debate basically says that a fetus isn't a "life" until a certain point in time (16 weeks, 3rd trimester, birth, whatever). Up until that point, the fetus is just a collection of cells that belongs to the woman, like fingernails or hair. Another person doesn't have a say over what you do with your fingernails or hair, so they shouldn't have a say over what you do with your "non-life" fetus.
Not saying I agree with that. I think the father should get some sort of say, but I don't know how to balance that with the rights of the woman. It's not exactly uncommon for a woman to use abortion as a means of retaliation. How would you feel if you got into an argument with your wife and she aborted your 3 month fetus to get back at you? It's happened to someone I know.
I don't know that I really agree with the "non-life" argument. Yes, a fetus can't survive on its own before the CNS develops. Some people compare this to euthanasia for people in a permanent vegetative state. Not really the same thing though. I doubt anybody would support taking someone off of life support if you knew for a fact that they would come out of it in 6 months and be a normal functioning person. I don't really see a difference between that and aborting a fetus.