You will never have a definitive answer outside of your own preconceptions. This is the same debate as gun control: "well it's wrong because I think A." "Yeah, well, I thinks it's right because I think B." The argument is based solely on what you think is right, not what you know is right.
Currently, the law states that a fetus is not a person. Until that is changed, no one, except the father of the baby (assuming the father is there and gives a damn, because there's a chance they aren't and don't) and the mother of the baby has any right to dictate the life of that baby. Not you, not me, not your religion. You aren't having the baby. Your life isn't going to be potentially ruined/come to a screeching halt if you have the baby.
I could list a big long list of variables to consider, like rape, how ready the mother actually is, would she be able to care for it, etc. But you know what, I won't, because you know them. Everyone does. And if anyone thinks for a second that a woman wouldn't be petrified at the prospect of having a completely unexpected pregnancy at a time where they are not prepared for one, then you need to go sit in the corner and think to yourself about how stupid you are. You can't simply decide for someone when they are ready for a baby. It is the opposite of ethical, and if you find some sort of moral justification for dictating such, then by all means, let me hear it. No I don't care how "alive" a fetus is. While life is beautiful, I don't think a girl in college who has big plans for her future would be thinking about how fantastic it would be to have to support a child. That would be the same as sacrificing one life for another, and while the concept is noble, the reality is that the fetus does not give one single damn about the mothers life. It simply grows until it is born. A fetus does not have a future to think about, it does not have bills to pay, degrees to get, graduate schools to go to. One day, it could. But at the cost of destabilizing the mothers life, and preventing her from reaching her goals and dreams? No. It would be trading potential for potential.
What would happen if abortions are outlawed? Any woman that gets pregnant is required by law to have the baby. Orphanages would see an increase in orphaned children, for one. But what about politically? If the government realizes it can dictate what a woman can and cannot do with her body (and also her creation), where would it end? Would it end there, or would we go into 1984 territory? In this day and age, if you think it would end there, you have a naivety I would love to have. Not because I have no faith in humanity (in fact, I do very much hope for humanity), but because when faced with the prospect of being able to control people, I very much doubt the government would turn that sort of power down.