I have a question for you on this subject:
Let's say a woman is pregnant and she doesn't want the child. But she can't get an abortion for one reason or another (too expensive, religious reasons, social reasons, legality etc.). So she is forced to raise this child, this unwanted accidental child. How do you think this child is going to feel growing up? Do you think he/she will be loved? Not always. It's possible, but it's unlikely, because the mother wanted to abort. Now is that fair for this child? And don't say "adoption" because orphanages are overcrowded enough as it is and as a result the conditions are often quite poor and children are not raised in proper loving circumstances they deserve.
Another point is overpopulation. We are expected to have 10 billion people on this planet by I think it was 2015 but I'm not sure. How are we going to deal with that and how are we going to slow down this growth? We can't murder people on the street - but if we make abortion easy and cheap to get we can a) contribute to population decay and b) conduct a lot of stem cell research to help people WHO ARE GROWN ADULTS, NOT FOETUSES, who are dying from currently incurable diseases and medical conditions.
I would like to refer you to
this video for a more educated argument for my position.