Here's my personal take on the issue.
Just so y'all know, I'm adopted.
According to the records, my birthmother was 18, and my birthfather was in his forties. According to my mom (who, while she has always been open about where I came from, may be trying to paint a prettier picture of things), she was the babysitter for his 9 year old son, things got out of hand, and she "went to visit an aunt" with only her mother and the guy knowing (and, supposedly, him supporting her financially throughout all this).
This wasn't a life-or-death situation. She chose not to abort me and to give me up for adoption. Yet whatever I accomplish in my life, I could not, would not be so fucking selfish as to DEMAND that that 18 year old girl give up 9 months of her life, her education, risk her life and well-being, undergo the permanent bodily changes of pregnancy, go through labor, give up her born child, in all likelihood suffer horribly every Mother's Day and my birthday for years, have to hide her burden from the family it was kept secret from....
All that, just for the potential, not reality, of my life. I wouldn't have known any different. And it probably would be better for her (possible) other kids if she didn't have me floating in the back of her head. Again, I'm not selfish enough to be glad she made this choice. That doesn't mean I don't enjoy my life (although reading political blogs and slogging through classes sometimes makes it difficult, heh) , and, no, I don't have any sort of self-loathing regarding all this. I'm here, and I'll do the best I can during my time on Earth. But I have a lot of empathy for that poor girl, and I wouldn't hesitate to council another girl in the same situation to do what is best for them.
This is why I'm pro-choice.