Why stop there? You have no idea, right? So why do you masturbate or use condoms? You're killing millions of potential babies!
Not the guy you're responding to, but you have a point. Coincidentally, most religions are also against both, so at least you can't accuse them of being inconsistent on the issue of reproduction.
Perhaps, but it will likely at least severely reduce it. It's certainly not appropriate to assume that every woman who would have had an abortion when it's safe and legal would also do so when it's dangerous and illegal. More likely, it would lead to a rise in babies given up for adoption.