I started out pro-life because as an evangelistic Christian it was the moral highground, then too leaned pro-choice because I didn't feel it was the governments responsibility to determine our ethics and tell us we couldn't kill if we chose. At the moment, I am not terribly compassionate, and could still kill someone in cold blood if I felt justified. I'm working on that, because nurturing compassion is the buddhist thing to do. However, I've never found justification in killing innocents, especially the very old and very young.
I don't think people have the 'right' to choose whether their offpsring lives or dies. You as an adult wouldn't want me to have the right to put my '45 to your forehead and blow it apart on a whim, simply because I felt you were a burden on me or society and I didn't want you around.